Disclosed are herbicidally active pyrimidine derivatives of the formula ##STR1## wherein R represents a hydrogen atom or an etherifying group, e.g., a lower alkyl, lower alkenyl, lower alkynyl, phenyl-substituted lower alkenyl, lower haloalkenyl, cycloalkyl, substituted phenyl-substituted lower alkenyl or phenyl-substituted lower alkynyl group; or a group represented by the following formula: ##STR2## wherein R.sup.1 represents a hydrogen atom or a lower alkyl group, X a halogen atom or a lower alkyl or lower alkoxyl group, m and n individually 0-2, and when m is 2, both Xs may be the same or different, and herbicidal compositions containing the same, alone or in combination with another herbicidally active compound, the pyrimidine derivatives being prepared by reaction of 2-(4,6-dimethoxy-2-pyrimidinyloxy)benzaldehyde with NH.sub.2 OR or with a salt of hydroxylamine followed by reaction with a halide of the formula RY wherein R has the same value as above and Y is Cl, Br or I.