The purpose of this paper is to study the biostability of PTT samples as an implantable biomaterial. In this study accelerated hydrolytic and enzymatic degradation tests were performed on PTT filaments so as to predict the relative rates of in vivo biodegradation. PTT filaments were subjected to a highly alkaline environment (pH 13.5) for periods of up to 10 days, and to PBS buffer and neutral enzymatic papain solutions for up to 9 weeks. Changes in weight loss, surface appearance, filament diameter, thermal properties, infra-red spectrum and tensile modulus were monitored over these time periods. PET samples were also exposed to the same solutions as a comparison to PTT samples. The results show that PTT filaments are more stable in alkaline solution, but less stable in PBS neutral buffer and enzymatic papain environments compared to PET filaments. The decrease of tensile moduli of the degraded PTT samples confirms the decrease of crystallinity and conform change of the trimethylene glycol conformers during the degradation.