Background: Mycobacterium marinum is a ubiquitous, slow-growing nontuberclosis Mycobacterium (NTM), it can causes disseminated granulomatous infections in fish. Outbreaks in fisheries can be financially devastating and can also increase the chance of human exposure.Objectives: The aim of this work was evaluating the effects of some environmental stresses on M. marinum CCUG 20998.Methods: In this descriptive-analytic study M. marinum CCUG20998 was subjected to different conditions of environmental stresses such as pH, oxidative, osmotic pressure, and temperatures. The effects of stresses were studied on growth, biofilm formation, and cell division and biochemical characteristics ofM. marinum CCUG 20998.The growth data were analyzed by measuring colony forming unit (CFU) using SPSS software version 19.Results: The results showed that sodium chloride and hydrogen peroxide at %10 and 9600 ppm concentrations inhibit. Marinum CCUG20998 growths, respectively. Tolerance topH=11 and temperature at 82.5°C was detectable. Also, environmental stresses could affects on some biochemical characteristics ofM. marinum CCUG20998. Biofilm formation reduced upon using all stress conditions.Conclusions: Bacteria are able to adapt to dramatically different environments, In the case of mycobacteria, there is direct correlation between stress and pathogenicity. The results obtained from this study provided useful information on survival and tolerance ofM. marinum CCUG 20998 to different environmental conditions. Survival under stress conditions might not reflect the in vivo situation where host factors also contribute to establishment of the organism during infection.