Mushrooms are rich in phenolic compounds. The extraction of bioactive compounds from oyster mushroom (Pleurotus citrinopileatus) using ultrasonication was optimized. Central composite rotatable design was conducted to optimize the extraction of polyphenols in water and ethanol. The independent variables taken for extraction were temperature (30–55°C), ultrasonic treatment time (8.00–20.00 min) and solvent/solid ratio (20–50 mL/g) and the responses were total phenolic content, total flavonoid content, 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging activity, and ferric reducing antioxidant property. The parameters of ultrasonication frequency and power were kept constant. The optimized conditions for water extract were 44°C, 14 min, and 20 mL/g and that of ethanol extract were 39°C, 13 min, and 20 mL/g. Ultrasonication treatment time, temperature and solid to solvent ratio influenced the yield of phenolic acids which were reflected in the responses analyzed. The experimental values under optimal conditions were in good agreement with the predicted values. The study demonstrated that mushroom extract obtained by ultasonication has potential for its health beneficial properties. Practical Applications Mushroom is a very good source of bioactive compounds. But being perishable in nature, it loses its functional properties very quickly after harvesting. The bioactive compounds can be extracted from mushroom and can be incorporated in different foods for their enrichment. This study showed that ultrasound‐assisted (UAE) extraction has potential as an emerging technique for extraction of bioactive compounds from plant sources. UAE showed higher yield of polyphenolic compound with higher antioxidant activity as compared to the conventional extraction methods. Moreover, UAE resulted in less consumption of time and energy than the conventional methods. The results indicate that ultrasound assisted extraction can be promoted as a extraction technique by different food industries.