Abstract Polycaprolactone (PCL) is a semi-crystalline polymer and belongs to a biodegradable plastic. PCL also can naturally degraded, has a high degree of adjustment with other polymer, and has great mechanical and thermal properties. By using the Lewis acid catalyst, PCL can be yielded through the ring opening polymerization (ROP) of caprolactone (ε-CL). The objective of this study was to explore the most likely reaction mechanism of the ROP of ε-CL using bis(dibenzoylmethanato) zirconium(IV) chloride as a catalyst. Here, the Hyper Chem 8.0 program was performed to compute the monomer molecule, intermediate molecules, and polymer molecule. The program can be launch on the Windows 07 systems. The method used was the PM3 semi-empirical method. This program also used to show the results of optimized structures. The calculation results show that to generate PCL required bis(dibenzoylmethanato) zirconium (IV) catalyst. The ROP reaction mechanism of ε-CL can be occurs through direct coordination ε-CL on the Zr complex. After that, deprotonation and insertion monomer. Last step was chain propagation of the χ–CL.