A process for preparing 2-unsubstituted imidazoles which comprises reacting an .alpha.-hydroxycarbonyl compound with a formamide in such amounts as to make the molar ratio of said formamide to said hydroxycarbonyl compound not more than 2 at a reaction temperature of 100.degree.-170.degree. C. in an atmosphere of ammonia gas. According to this process, 2-unsubstituted imidazoles may be obtained in very high yields. In addition, because no great excess of formamide is used in carrying out the reaction, an effect of not requiring the recovery operation incident to decomposition of formamide is obtained as well. And by removing formic acid formed as a by-product by the reaction, a reactor and separation equipment such as a distillation column are not corroded, and imidazoles of a high purity can be obtained.