Abstract: Fifteen novel title compounds were synthesized from 3-(4-methyl-1,2,3-thiadiazolyl)-4- amino-1,2,4-triazolo-5-thione with substituted benzaldehyde in acetic acid under refluxing.The structures of the compounds were confirmed by elemental analysis,IR and 1H NMR.The single crystal of compound 5c was cultured and determined by X-ray single-crystal diffraction as of a monoclinic system,space group P2(1)/c with cell parameters a=1.403 7(3) nm, b=1.570 5 (3) nm,c=0.686 4 (4) nm,β= 102.06 (3)°,V=1.479 8(9) nm3 ,Z=4,F(000)=656.Bioassay was conducted by fungi growth inhibition method using 10 commonly used fungi which represented most disease occurring in China,the results showed that,all the title compounds had satisfactory fungicidal activity against Botrytis cinerea,the growth inhibition rate of compound 5l against Botrytis cinerea was up to 87%,for compound 5c,5d and 5f were more than 78%,compound 5a exhibited fungicidal activity against Gibberella zeae with growth inhibition of 78.7%,the growth inhibition rate of compound 5m against Colletotrichum lagenarium was 65.6%.