In search of novel herbicides with high activity, a series of 2-arylthio-1,2,4- triazolo [1, 5-a ] pyrimidines (3) were synthesized by cyclization of 5-amino-3-arylthio-1,2,4-triazoles with 1,3-diketones or by the nucleophilic substitution of substituted thiophenols with 2-methylsulfonyl-1, 2, 4-triazolo [ 1, 5-a]-pyrimidine. The structures of all compounds prepared were confirmed by 1H NMR and MS spectroscopy along with elemental analyses. Preliminary bioassays indicated that some of the compounds 3 had good herbicidal activity against rape. In addition, the regioselectivity in the reaction of 5-amino-3-sub-stituted arylthio-1,2,4-triazoles with benzoylacetone was studied. In a search of novel herbicides with high activity, a series of 2-arylthio-1,2,4- triazolo [1,5-a] pyrimidines (3) were synthesized by cyclization of 5- amino-3-arylthio-1,2 , 4-triazoles with 1,3-diketones or by the nucleophilic substitution of substituted thiophenols with 2-methylsulfonyl-1,2,4-triazolo [1,5-a] -pyrimidine. NMR and MS spectroscopy along with elemental analyzes. Preliminary bioassays indicated that some of the compounds 3 had good herbicidal activity against rape. In addition, the regioselectivity in the reaction of 5-amino-3-sub-stituted arylthio-1,2,4 -triazoles with benzoylacetone was studied.