Poly(-caprolactone) (PCL) is an aliphatic biodegradable polyester that has glass transition and melting temperatures around -60 ̊C and 60 ̊C, respectively. PCL can be synthesized via ring opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL). In general, organometallic compounds are used for chemical synthesis and lipases are used for enzymatic synthesis. In this study, modification of rice husk ash is achieved by trimethoxysilylpropyl ethylene diamine (TMSPDEA) and then Candida antarctica lipase B (CALB) is immobilized onto modified rice husk ash. This system is used as an enzymatic catalysis for ROP. Polymerization reactions were carried out at various temperatures (i.e., 30, 40, and 60 ̊ C) and times (i.e., 6, 24, and 48 hrs). Reaction was terminated by the addition of chloroform to the mixture and then enzyme was separated from the reaction mixture by filtration. Subsequentely, chloroform was evaporated at 50 ̊ C in an oven. The polymer was then precipitated by addition of cold methanol. The polymer samples were washed with methanol and filtrated. At the end, the polymers were dried at 35 ̊ C to get the final product. With determined optimum temperature and time, the effect of enzyme concentration (i.e., 2.5, 5, 10%) on the ROP of PCL was also investigated. In order to obtain reuse capacity of immobilized enzymes for ROP, enzymes were seperated from the reaction mixture, washed by phosphate buffer (pH: 7, 0.015 M), and eventually dried in the oven. Therefore, these enzymes could be used again under optimum polymerization conditions. Gel permeation chromatography (GPC) was used to determine the moleculer weight and polydispersity index values; Fourier transform infrared spectroscopy (FTIR) was also utilized to determine the chemical structure; and thermal gravimetric analyzer (TGA) and differential scanning calorimeter (DSC) were used for thermal characterization of polymers.