Drought is an insidious environmental phenomenon which is more pronounced in arid and semi arid regions. Central eastern, and southern regions of Iran are characterized as arid, and semi arid climate. Precipitation variability in the Sistar and Balouchestan Province is very high. This is due to remoteness from Mediterranean cyclonic trajectory and the predominance of a subtropical high pressure system Accordingly, the Sistan and Balouchestan is more prone to drought than other provinces in Iran. In this paper, the probability of drought occurrence and extent in this province is investigated applying lag-1 Markov chain on SPI time series in 3- and 6-month time scales. The results showed that the probability of drought persistence; based on 6-month SP time series, is higher than 70 percent in central portion of the province and decreases to 50 percent moving east Considering the drought equilibrium probability, the result: also indicated that the central district of the province an affected by drought events 30% of the time and therefore is more vulnerable to drought conditions compared to other regions in the province.