The mycelial growth rate of three oyster mushroom strains namely Pleurotus erengii, P. ostreatus and P. florida was examined on six different agar media (malt extract, Potato dextrose, rose bengal, corn meal, czapek's dox and waksman's glucose agar media) to select the most suitable one. Effect of pH was also examined at different values (5.0, 5.5, 6.0, 6.5 and 7.0) on the selected medium. Results indicated that Malt extract agar medium was the most suitable one for mycelium growth of all the tested mushroom strains, being the highest (9 cm ) for P. erengii and P. ostreatus at pH 7 and 9 cm at pH 6 -6.5 for P. florida after 6 days of incubation. The mycelia growth of the tested oyster mushroom strains was also examined at different temperatures (15, 20, 25, 30 and 35ºC) and different levels of relative humidity (50, 65, 75, 85, 95 and 100 %) on malt extract agar medium. The highest mycelial growth rate was obtained at 25°C and relative humidity of 65% after 6 days of incubation for the three tested oyster mushrooms.