Pleurotus ostreatus have been used as a traditional remedy and food source. Its anti-inflammatory, anti-oxidation effects have been previously reported. The production of cytokines (IL-$2{eta}$, IFN-${gamma}$, and TNF-${alpha}$) secreted by LPS- and non LPS-stimulated macrophages, were detected by ELISA assay using a cytokine kit. Mouse splenocytes proliferation increased with Pleurotus ostreatus water extracts supplement at 5, 10, 50, 100, 250, 500, $1,000{mu}g/mL$ after a 48hr pre-treatment with the mitogen (ConA or LPS). The cytokine production (IL-$2{eta}$, IFN-${gamma}$, and TNF-${alpha}$), measured by a cytokine ELISA kit, increased on water extracts supplementation. This in vitro study suggested that supplementation with Pleurotus ostreatus water extracts may enhance the immune function by regulating the splenocyte proliferation and enhancing cytokine production.