A process for producing a thiazole compound of the formula (3): wherein X1 is a hydrogen atom or a halogen atom, which comprises reacting a compound of the formula (1): wherein X1 is as defined above, and X2 represents a halogen atom, with ammonia and formaldehyde to obtain a hexahydrotriazine compound of the formula (2): wherein X1 is as defined above, and reacting the resulting hexahydrotriazine compound with hydroxylamine under acidic conditions. According to this process, the thiazole compound of the formula (3) can be industrially advantageously produced using inexpensive ammonia with suppressing the formation of a byproduct of the formula (4): wherein X1 is as defined above.