A process for purifying octafluoropropane according to the present invention includes the step of contacting a crude octafluoropropane containing impurities with an impurity decomposing agent under an elevated temperature and then with an adsorbent to substantially remove the impurities from the crude octafluoropropane. According to the purification process or preparation process of octafluoropropane of the present invention, impurities such as chlorine compounds can be substantially removed and a high-purity octafluoropropane can be easily obtained. The octafluoropropane obtained by the purification process of the present invention is substantially free of impurities and, therefore, can be used as an etching or cleaning gas for use in the production process of a semiconductor device and the like.