In this study, we have investigated in vitro the alkaline and enzymatic hydrolysis of enantiomeric mixtures from l-PLA and d-PLA at the air/water interface. It was founded that the hydrolysis rate of stereocomplexed-mixture monolayers from l-PLA and d-PLA was much lower than those of their homopolymers, regardless of degradation mediums. The retardation of hydrolysis is mainly due to strong interaction between d- and l-lactide unit sequences, which prevents the penetration of degradation mediums into the bulk. To conform this behavior of stereocomplexes, hydrolytic behaviors of solution-cast thin films were also investigated. The result was well consistent with monolayer's behavior.