Abstract: ObjectiveThe chemical compositions of Macrolepiota detersa were analyzed and its antioxidant activity was evaluated to provide theoretical references for its development and utilization . MethodVolatile oil and acetone crude extract were obtained from fresh fruit bodies of M. detersa by acetone extraction and vacuum rotatory steam distillation. Chemical compositions of the volatile oil were analyzed by gas chromatography-mass spectrometry (GC-MS) method,and chemical constituents of acetone crude extract were analyzed by pre-test tube method. Antioxidant activity of acetone crude extract was evaluated by free radical scavenging experiment. ResultGC-MS results showed the main components in the volatile oil were ketone compounds, and the main component 4-hydroxy-4-methyl-2-pentanone accounted for 86.32%. Acetone crude extract contained alkaloids,sterols,and terpenes according to pre-test tube method. Free radical scavenging experiment indicated that acetone crude extract contained antioxidant activity, and half maximal effective concentration (EC50) values of·OH radical scavenging activity was 260.45 μg/mL while EC50 values of·DPPH radical scavenging activity was 552.87 μg/mL. ConclusionThe main components in volatile oil of M. detersa include seven ketone compounds, one alcohol compound and one ester compound. Acetone crude extract contains alkaloids, sterols, and terpenes, thus embodies antioxidant activity. Therefore M. detersa is worth further development.