A process for producing a 2-alkenyl-3-aminothiophene derivative represented by any one of the general formula (3a) to 3(d) or a mixture thereof, comprising contacting a salt formed from a 3- aminothiophene derivative represented by the general formula (2) and an acid with a ketone derivative represented by the general formula (1) to obtain the 2-alkenyl-3-aminotliiophene derivative, wherein the ketone derivative is in the amount of not less than 1 mole equivalent based on the amount of the 3-aminothiophene derivative
