Poly(p‐dioxanone) (PPDO), a typical aliphatic poly(ether‐ester), is generally synthesized via ring‐opening polymerization of 1,4‐dioxan‐2‐one (p‐dioxanone, PDO) monomer. However, a quite amount of PDO monomer should coexist with PPDO product due to the characteristics of the equilibrium polymerization. To clarify the effects of PDO on the properties of PPDO, a series of PPDO/PDO mixtures with different PDO content were prepared by adding PDO to pure PPDO. The thermal, mechanical, and hydrolytic properties of PPDO and PPDO/PDO mixtures were investigated systematically. It reveals that the existence of PDO in the polymer can act as plasticizer to facilitate the crystallization of PPDO, but the increasing of PDO content deteriorates the mechanical properties of the polymers, especially when the PDO loading is more than 3 php. The PDO does not distinctly affect PPDO thermal decomposition, but obviously accelerates the PPDO hydrolytic degradation. This work may provide an important reference for the industrialization and application of PPDO. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43483.