This paper presents a new approach for studying the hydrolytic degradation kinetics of biodegradable polymers using time-of-flight secondary ion mass spectrometry (ToF SIMS). In this study, in vitro hydrolytic degradation of polyglycolic acid (PGA) has been carried out at 37 degrees C in aqueous saline buffer solutions of different pH values. The molecular weight distribution of hydrolysis products was obtained from the ToF SIMS spectra. The average molecular weight of the hydrolysis products calculated from the ToF SIMS spectra is a function of hydrolysis time. Hydrolysis kinetics equations for PGA based on solid/liquid heterogeneous reaction conditions are established. A good linear relationship was obtained using this kinetics equation. The reaction rates observed in this study generally agree with observations reported in the literature. Kinetics constants for the hydrolytic degradation of PGA at different pH values have been obtained. This new approach demonstrates that ToF SIMS can be a powerful and fast technique in the study of degradation kinetics of biodegradable polymers. Using ToF SIMS, the hydrolysis kinetics of biodegradable polymers can be explored in the range of hours with in-vitro methods.