A new method to study water uptake into biodegradable polymer was developed. Polymer was gently mixed with the tritiated buffer and the radioactivity level of the polymer due to water uptake was measured by liquid scintillation counting. The rate of water uptake was estimated from the plot of the amount of water in the device as a function of time. The technique used in this study is particularly useful for estimating water uptake of biodegradable polymers which were difficult to study by other techniques such as weight gain used for hydrogel.