Abstract: In this study, the low temperature saponification treatment was used to hydrolyze the astaxanthin (Asta) extracts of Penaeus sinensis. Further, the changes of total Asta concentration, antioxidant activity, free form and ester form of Asta and its optical isomerswere compared before and after saponification. The results showed that proper saponification treatment significantly increased the total Asta concentration of the extracts. Moreover, the saponification time played crucial roles on the in vitro antioxidant activity of the Asta extracts (P<0.05). The scavenging activity of the Asta extract on DPPH free radical was 28.85% after 2 h of saponification, significantly higher than 15.16% of un-saponified. The activity of scavenging hydroxyl free radicals and total antioxidant capacitywere increased to 3.17, 0.62 U/μg, respectively, after 6 h of saponification.The results of HPLC analysis demonstrated that most of Asta esters were transferred into free Asta after 2 h of saponification. Further, the free Asta producedwas destroyed in some degree when exposed to long time saponification. The optical isomer in the un-saponified Asta extracts was mainly composed of 3S, 3´S. In the process of saponification, the relative content ratio of the relative content ratio of 3S, 3´S:3S, 3´R:3R, 3´R was maintained between 2.4:1.5~1.7:1.0. Further, the three optical Astaisomers in saponification solutions had high linear correlations with their scavenging activities on hydroxyl free radicals (R>0.784). In conclusion, the changes of antioxidant activity of astaxanthin extracts from the saponified Penaeus sinensis were related to the changes of free and ester astaxanthin composition and optical isomer composition.