The method of preparing a chromium oxide catalyst for preparation of pentafluoroethane using a chloroethane compound includes heat treating chromium hydroxide powder at a temperature not higher than 300.degree. C. to obtain chromium oxide powder, heat treating metal hydroxide, at a temperature not higher than 300.degree. C. to obtain metal oxide powder, mixing 85.about.99.5 wt % of the chromium oxide powder with 0.5.about.15 wt % of the metal oxide powder to obtain a mixture, forming the mixture into a pellet, calcining the pellet at 200-300.degree. C. using nitrogen gas, and fluorinating the pellet at 300-320.degree. C. using a gas mixture including N.sub.2 and HF, and then at 320-380.degree. C. using HF gas. The fluorination catalyst prepared using the method of this invention can be effectively used to prepare pentafluoroethane at a high yield using a chloroethane compound.