A commercial calcium dimethoxide and an in-situ generated calcium methoxide prepared from bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide] and methanol, were investigated as initiators for the ring-opening polymerization of epsilon -caprolactone and L-lactide. Commercial calcium dimethoxide initiated rapid epsilon -caprolactone polymerization at 120 degreesC in bulk to give quantitatively a polymer with a polydispersity index around 1.3. Significant racemization was observed for L-lactide polymerization. The In-situ formed calcium methoxide promoted the solution polymerization of both epsilon -caprolactone and L-lactide to high conversion at room temperature over a short time period, yielding the corresponding polyesters with narrow molecular weight distribution. NMR spectra showed that the poly(L-lactide) isolated had a purely isotactic microstructure. The initiator efficiency could be tuned by varying the molar ratio of methanol and bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide].