To obtain basic information on the stability, decomposition, and recycling of biodegradable polyurethane foam (PUF), we studied hydrolysis and aminolysis of the PUF derived from wattle tannin (WT). The WT-PUF exhibited almost the same stability to a hydrolytic treatment at room temperature as trimethylolpropane (TMP)-PUF, which was prepared by cross-linking with TMP. Weight loss and strength loss of WT-PUF were much larger than those of TMP-PUF during the hydrolytic treatment at an elevated temperature. Hydrolysis was mainly responsible for the cleavage of urethane bonds to form WT and amines at the initial stages of the treatment. At the later stages, however, urethane bonds seemed to be cleaved not only by the hydrolysis but also by aminolysis with the amines formed in the system.