Abstract: The MOPAC-AM1method was employed to optimize the molecular geometries of thirteen 3-substituted sulfur-5-(2-hydroxy-phenyl)-4H-1,2,4-triazole compounds.It was also used to calculate quantum chemical descriptors(L_t) such as E_HOMO,E_LUMO,Q_C1~Q_C8,Q_N1~Q_N3,Q_O and Q_S of the compounds.The antibacterial activities(I_J: I_M,I_E and I_S) of these compounds to Monilia albican,Escherichia coli and Staphylococcus aureus along with the above descriptors were used to establish the quantitative structure-activity relationships(QSAR) with leaps-and-bounds regression analysis.It shows that the E_LUMO and Q_S affect the bioactivities of these compounds directly.The insecticidal activities of the compounds increase with the increase of the Q_S;however,the higher the E_LUMO is,the lower the I_J is.The correlation coefficients(R²) and leave-one-out(LOO) cross validation R_cv² were 0.913 and 0.806 for I_M model,0.907 and 0.838 for I_E model,0.881 and 0.771 for I_S model,respectively.The QSAR models have both favorable estimation stability and good prediction capability by using R_adj²,F,R_cv²,VIF,AIC,FIT tests.The results present important information for the antibacterial mechanism and will be useful for theoretical designing new active title compounds.