The mycelia! biomass production of four strains (WS218-1, WS218-2, CST01, and CST02) of Pleurotus cystialosus in liquid culture using coconut water as a medium was evaluated. Mycelia were extracted and the 1,1-diphenyl-2-picrylhydrazyl radical scavenging activities and total phenolic contents were analyzed. The mycochemicals of the best strain were also screened using a thin-layer chromatography spot test. Results revealed that WS218-2 strain produced the heaviest mycelial biomass (6.57 g fresh wt. and 039 g dry wt.) while CSC02 and WS218-1 strains registered the lowest fresh and dry weight, respectively. Ethanolic extract of the WS218-2 strain showed the highest radical scavenging activity (79.01%) and contained the highest phenolic content (95.67 mg gallic acid equivalents/g of sample). Eleven mycochemicals including essential oil, triterpenes, anthraquinones, tannins, flavonoids, phenols, fatty acids, alkaloids, steroids, sugars, and coumarins were detected in WS218-2 mycelia. Pleurotus cystidiosus mycelia could be a valuable source of natural antioxidants and bioactive metabolites and it is strain-dependent.