Copolymerization of glycolide (GA) and 6(R,S)-methylmorpholine-2,5-dione (MMD) was carried out in bulk using stannous octoate as an initiator. The effects of temperature, time, concentration of stannous octoate, and the feed composition on the copolymerization were investigated. DSC analysis showed that glass transition temperature (T-g) of the resulting copolymers (PGM) increased with increase of MMD content in the copolymers, while melting temperature (T-m) and heat of fusion (Delta H) decreased. In vitro degradation was performed in two media : PBS buffer (pH 7.4) and distilled water (pH 6.8). It showed that the erosion rates increased with increasing MMD content in the original copolymers, and the degradation proceeded more rapidly in PBS buffer than in distilled water. Based on the changes of composition and crystallinity of the samples during the degradation, it is suggested that the degradation proceeded through two main stages : first, mainly in amorphous regions and then in crystalline ones.