L-lactide was prepared from L-lactic acid with stannous octoate as the catalyst. The effects of reaction temperature and pressure on the ingredient of crude lactide were investigated. The results show that the mass fraction of meso-lactide increases with the increasing reaction temperature. Crude lactide containing 85.4% L-lactide is obtained when the reaction temperature is 200 ℃. High purity of L-lactide with a yield of 40.6 % is obtained by synthetic purifying method. The properties of L-lactide are characterized by optical purity, infrared spectrum and gas chromatogram/mass spectrum. The L-lactide samples purified by recrystallization and synthetic purifying methods are polymerized with the catalyst of stannous octoate, and the corresponding viscosity average relative molecular masses of poly(L-lactide) are 2.85 × 105 and 5.05 × 105 , respectively. This indicates that the optical purity of Llactide has great influence on the relative molecular mass of poly(L-lactide).