Abstract: A method for purifying an unsaturated fluorocarbon compound includes causing a crude unsaturated fluorocarbon compound shown by the formula C5F8 or C4F6 to come in contact with a boron oxide to obtain a purified unsaturated fluorocarbon compound. A method for forming a fluorocarbon film includes forming a fluorocarbon film by a CVD method using the purified unsaturated fluorocarbon compound as a plasma reaction gas, and a method for producing a semiconductor device includes a step of forming a fluorocarbon film by a CVD method. Because the purified unsaturated fluorocarbon compound obtained by the above method has a high purity and an extremely low water content, the compound may be suitably used as a plasma reaction gas for forming a fluorocarbon film using a plasma CVD method or a plasma reaction gas used for a semiconductor device production process including a fluorocarbon film formation step by a CVD method.