Ownership dispersion is an important effective factor in determining bid-ask spread. Bid-ask spread has important role in STOCK LIQUIDITY. Some researches indicate that increasing in ownership dispersion leads to decrease bid-ask spread and therefore increase STOCK LIQUIDITY. No many researches have done about the relationship between ownership dispersion and bid-ask spread in Iran. Therefore the main goal of this paper is to review the relationship between ownership dispersion as an independent variable and bid-ask spread as dependent variable in Tehran STOCK Exchange. Therefore 156 firms that their required data for a seventh year period was available were studied. The multivariate pooled regression model is used to examine the hypotheses. The conclusions indicate that there is no significant relationship between ownership dispersion and Bid-Ask Spread in Tehran STOCK Exchange.

STOCK LIQUIDITY risk can be thought as one of the factors affecting the investors expected return. Clarifying a measure according to the specifics of the company to measure the STOCK LIQUIDITY could help the investors to make better decisions. In this study, we examine the relationship between assets LIQUIDITY and STOCK LIQUIDITY in hole of druggist firms listed in Tehran STOCK Exchange during the years 1387 and 1388. We use the turnover ratio .The results show that there is a significant relationship between the assets LIQUIDITY and STOCK LIQUIDITY. This relationship depends on market expectations regarding the deployment of the firm's liquid assets. Thus our hypothesis links STOCK LIQUIDITY to managerial actions that change the LIQUIDITY of the firm's assets, such as investment financing, and payout. Consistent with my prediction, I find that after controlling for firm fixed effects, increase in asset LIQUIDITY increases STOCK LIQUIDITY, too. The relation is stronger when the manager is less likely to convert liquid assets into illiquid assets such as for low market to book, during economic recessions, and when expected payout is high.

The individual Characteristics of managers such as optimism, abilityand CEO tenure can improve corporate financial performance, also can affected the behavior and the type of decisions makingin organization. Information transparency is affected by these behavioral Characteristics. The CEO tenure as a criterion is extent of decision making horizon of managers. In this research ability, tenure and optimism are used as individual Characteristics of managers. The sample of this study includes information on 100 companies accepted in Tehran STOCK exchange during 2013-2017. The results of data analysis indicated that the behavioral Characteristics did not have a significant effect on STOCK market inefficiency.

Earnings quarterly announcements in Tehran STOCK Exchange has increased during the past years. We examine the relation between quarterly earnings surprises and STOCK LIQUIDITY. We used effective relative bid ask spread as a proxy for STOCK LIQUIDITY. Based on the market model, this study compared abnormal effective relative bid ask spread and average abnormal effective relative bid ask spread in the period of 20 and 10 days before and after announcement. For a sample of 555 earnings quarterly announcement during 1384-1387 years, we show that STOCK LIQUIDITY has not increased around the earnings quarterly announcements.

Online Trading is a great transformation in capital market transactions, along with making access easy and decreasing transactions cost. This research aims to investigate the market behavior about Online Trading, before and after it has been legal. Statistical population includes all firms listed in Tehran STOCK Exchange and Iran Fara Bours (OTC) which have at least one trade in each month during March, 2009 and February, 2013. According to the limits, 3792 firm-month observations have been chosen which includes 79 highly traded STOCK. The results show that Online Trading has a significant positive impact on volume and count of trading STOCKs, so the STOCK LIQUIDITY increased after online trading has been legal. Although, Online Trading decrease the amount of abnormal return. Also, results show that online trading was effective on significant increasing the Bid-Ask spread.

According to predictions in the literature, sock price of firms with greater product market power is less sensitive to order flows which results in greater STOCK LIQUIDITY. This prediction was examined in a sample of 75 listed companies in Tehran STOCK Exchange during 1388 to 1391 using three ilLIQUIDITY measures (Amihud Ratio, Quoted Spread, Effective Spread) and two proxies for market power. The results of panel regressions showed that STOCK LIQUIDITY increases with market share (the first proxy of market power). Findings also showed the relationship between operational income ratio (second proxy of market power) and STOCK LIQUIDITY is not meaningful and consistent with theory. It seems that the reputation of firms in product market (respect to market share) results in higher STOCK market LIQUIDITY than their profitability. Other results confirmed that advertising in product market doesn’t influence STOCK market LIQUIDITY, directly.