The studies reported in this thesis represent an investigation of the physiological and biochemical studies of wild and exotic Pleurotus species. Comparison of the growth rates of different Pleurotus isolates showed that most of the strains grew at optimum temperature of 25°C, where as a temperature above 25°C detrimental to mycelial growth for Pleurotus species except Pleurotus sapidus wild isolated from Pakistan which can tolerate a high temperature upto 35°C. Among growing agar media, potato dextrose agar was a better medium than malt extract agar and wheat extract agar for the growth of mycelium of Pleurotus species. Pleurotus species grew best at pH 6.5 while, Pleurotus sapidus wild isolate from Pakistan showed wide range of pH acceptability. Pleurotus strains (wild and exotic) investigated differed in their growth rates on different substrates. Among the substrates cotton waste (100%) produced maximum yield and biological efficiency (%). Fruit quality of Pleurotus species in terms of pileus diameter, stalk diameter, stalk length and individual fruit body weight was also exhibited higher in cotton waste substrate. Among the Pleurotus species Pleurotus sajor-caju showed maximum yield and biological efficiency on cotton waste and its various combinations. Pleurotus sapidus, wild isolate from Pakistan showed fastest mycelial growth and its yield was also comparable to high yielding Pleurotus sajor-caju strain. Maximum number of flushes was also counted in Pleurotus sajor-caju on cotton waste (100%) substrate. The biochemical studies exhibited high nutritional value of Pleurotus species in terms of protein, carbohydrate, ash, fibers, energy, and fat percentage. Pleurotus ostreatus showed maximum protein percentage than other Pleurotus species, Pleurotus sapidus wild isolate also exhibited higher protein contents but less than Pleurotus ostreatus and Pleurotus sajorcaju. Different substrates influenced the nutritional value of Pleurotus species and cotton waste showed maximum nutritional value when used as substrate for oyster mushroom cultivation than other substrates. Among the mineral contents of Pleurotus species potassium was found higher in Pleurotus ostreatus on cotton waste than other substrates, other important minerals such as Mg, Mn, Ca, Zn, and Fe were also found in reasonable amounts. Total soluble solids (TSS), acidity, vitamin C, total phenolic contents and antioxidant activity were also higher in Pleurotus species, which revealed that Pleurotus species are good for health. In addition to these physiological and biochemical studies of Pleurotus species biochemical analyses of different substrates used in this study were also performed before and after oyster mushroom cultivation. A reasonable increase in the nutrient contents in terms of nitrogen, phosphorous, potassium and protein percentage was exhibited by spent substrate. Maximum increase in nutrient contents was shown by substrates when Pleurotus ostreatus was cultivated on them. Pleurotus sajor-caju showed highest score for taste and aroma. The results showed that cottonwaste is the best substrate for the cultivationof Pleurotus species.