Oyster mushroom (Pleurotus spp.) cultivation is a very simple low cost technology. Four Pleurotus spp. viz. P. ostreatus, P. florida, P. pulmonarius and P. flabellatus were grown in 30 ± 2⁰C in non-sterilzed rice straw. All the biochemical studies were done using 70% methanolic extract of dried powder of mushroom fruiting bodies. Flavonoids, total phenol, orthodihydric phenol content of all the species were measured in addition to their protein and carbohydrate contents. P. ostreatus showed highest protein and carbohydrate. P. flabellatus showed highest flavonoid. P. florida showed highest phenol content whereas P. florida and P. pulmonarius showed highest orthodihydric phenol contents. Antioxidant activities of the mushroom extract in terms of ABTS and DPPH oxidation and reducing power was estimated in all the species. Though ABTS scavenging activities are more or less similar but DPPH scavenging activities differ markedly in different Pleurotus spp. and P. ostreatus showed the highest result (74+2.2%). The highest reducing power was found in P. florida. The fruiting body as well as mycelial extract of Pleurotus species showed antibacterial activities in as low as 36-45 mg fresh fruiting body equivalent which is comparable to standard commercial antibiotic erythromycin. The present study does not establish the superiority of any single species but in general all the studied Pleurotus species contained different nutraceuticals which may be utilized for the benefit of nutritional as well as health status of people from third world countries.