Cyclic dimer of butylene succinate (CDBS) was purified from the crude cyclic oligomers of butylene succinate. The purified CDBS was characterized by 1H NMR spectrum and mass spectra. The purified CDBS was subjected to ring-opening polymerization (ROP) to obtain poly(butylene succinate) (PBS) with 1-dodecanol as the initiator and tin octoate as the catalyst. The resultant PBS was characterized by Fourier transform infrared (FTIR) spectroscopy and 1H NMR spectrum. The effect of ROP temperature, ROP time and catalyst content on molecular weight of PBS and conversion were also investigated. The results show that, ROP can obtain the high-molecular-weight PBS, the highest number-average molecular weight (Mn) reached about 63.3 kDa in 3 h at 220 °C.