Abstract: Embryogenic callus was induced from protocorm-like body(PLB) dice of Phalaenopsis spp.Embryonic cells occurred on the 11th-18th day of culture,and young globular-shaped embryoids appeared on the 25th-32th day.For the first 11 days,the relative content of · OH in cultures undulated slightly,O₂.production rate increased continuously and achieved its highest value,and H₂O₂ content increased significantly,meanwhile total antioxidative capability remained low.The results suggested that oxidative stress on explants was relatively high,which was advantageous to cell dedifferentiation and acquisition of embryogenic potential.In addition,SOD activity in the cultures showed an increasing tendency,and POD and CAT activities reached a peak.During the whole callus induction period,total antioxidative capability,DPPH scavenging capacity,and the H₂O₂ content generally continued to increase,and each showed a very sig-nificant positive correlation with SOD activity.Results indicated that SOD was the main factor that affected scavenging radical capability and increasing antioxidatioe of cultures.Comprehensive analysis of the experimental results suggested that SOD,O₂.,and H₂O₂ played important roles during the induction of embryogenic callus from Phalaenopsis spp.explants.