The present invention relates to a method for producing a pyrimidine derivate useful as a neurocyte neurocyte necrosis inhibitor and an intermediate thereof. Disclosed is a method for producing an acid salt of 4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine. The method comprises reacting 4-chloro-6-(4-fluorophenyl)-2-methylpyrimidine with 5-piperidino-1-pentanol, hydrating the thus obtained 4-(4-fluorophenyl)-2-mehtyl-6-(5-piperidinopentylox) pyrimidine and then converting the resultant the hydrate into an acid salt. The hydrate as a describe above; and a method for producing the hydrate is part of this invention. According to the present invention, a highly pure acid salt of 4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine can be readily and efficiently produced without using a column chromatography. Thus, this method is suitable for the production thereof on a industrial scale.