Disclosed is a method of purifying (Z)-1-chloro-3,3,3-trifluoropropene of the formula [1], comprising: distilling a mixture containing (Z)-1-chloro-3,3,3-trifluoropropene and 1-chloro-1,3,3,3-tetrafluoropropane (CF3CH2CHClF), wherein the distilling is performed by extractive distillation of the mixture in the coexistence of at least one kind of compound selected from the group consisting of halogenated hydrocarbons of the formula [2], halogenated unsaturated hydrocarbons, nitriles, ketones, carbonates, ethers, esters and alcohols as an extractant [Chem. 8] CFnCl3-nCHXCClFmH2-m  [2] where X represents a hydrogen atom (H), a fluorine atom (F) or a chlorine atom (Cl); n represents an integer of 0 to 3; and m represents an integer of 0 to 2.