The effect of polycarbodiimide (PCD) on hydrolytic stability of poly(p-dioxanoiie) (PPDO) was investigated by hydrolytic degradation of PPDO and PPDO added with PCD (PPDOCD) in phosphate buffer solution (pH = 7.4) at 37 degrees C. The variation of weight, water absorption, pH, molecular weight, tensile properties, surface morphologies, and thermal properties with degradation time were evaluated. After 11 weeks, the weight loss and water absorption of PPDO was 24 and 30%, respectively, but the corresponding values were only 3 and 5% for PPDOCD5, where 5 represents the weight percentage of PCD added; the molecular weight of PPDO decreased much faster than that of PPDOCD. The pH of the solution was monitored for 15 weeks and a final pH value of the solution involving PPDOCD5 was 6.81 whereas that of PPDO solution was 3.77, indicating that more acid fragments from PPDO samples migrate into the buffer solution. Surface morphological changes showed a better physical integrity for PPDOCD samples and they also kept their mechanical properties for a longer time than PPDO samples. These results revealed that PCD can retard the hydrolysis degradation of PPDO and enhance its hydrolytic stability. (c) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 3079-3086, 2009