Abstract: The present invention relates to novel pyrimidine derivatives of formula (I) or pharmaceutically acceptable salts thereof which possess an excellent anti-secretory activity, pharmaceutical compositions containing the same as an active ingredient, their novel intermediates, and processes for the preparation thereof wherein: when A is piperidin-1-yl or —NH—B, wherein B is C3-C4 alkyl, C3-C4 alkenyl, C3-C7 cycloalkyl, C1-C3 alkoxyethyl, phenylethl which may be substituted or unsubstituted, 3-trifluoromethylphenylmethyl, 1-naphthylmethyl, 4-methylthiazol-2-yl or 4-phenylthiazol-2-yl, R1 is hydrogen or methyl; and R2, R3, R4 and R5 are hydrogen; or when A is a group of formula (II); when R1 is hydroxymethyl or C1-C3 alkoxymethyl, R2, R3, R4, R5 and R6 are hydrogen; and R7 is hydrogen or halogen; or when R1 is hydrogen or methyl, R7 is hydrogen or halogen; and one or two of R2, R3, R4, R5 and R6 is hydroxy, methoxy, or a group of formula (III) wherein Z is C1-C4 alkyl, substituted or unsubstituted C1-C4