In a search for novel agrochemicals with high activity and low toxicity, a series of diheterocyclic compounds containing 1,2,4-triazolo[1,5-a]pyrimidine and 1,3,4-oxadiazole rings were designed and synthesized by a four-step synthetic route starting from 2-mercapto-5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine. The structures of all the compounds synthesized were confirmed by H-1 NMR, mass spectroscopy and elemental analysis. The preliminary bioassay against Brassica campestris L and Echinochloa crusgalli Beavu indicated that the title compounds displayed herbicidal activity at the concentration of 100 ppm and that compounds 5a (R = CH3), 5d (R = C2H5) and 5f (R = i-Bu) were found to have particularly high activities. In addition, the results of an in vivo test at a concentration of 50 ppm showed that all the compounds prepared were highly active against Rhizoctonia slain, but not active against Fusarium oxysporum, Gibberella zeave and Phoma sparagi. A further in vivo test showed that compound 5j possessed better fungicidal activity against Rhizoctonia solani at a concentration of 200 ppm than Carbendazim. and Validamycin A, which are well known for their fungicidal activity against Rhizoctonia solani. To our knowledge, this is the first report that 1,2,4-triazolo[1,5-a]pyrimidine derivatives display fungicidal activity against Rhizoctonia solani.