Abstract: A laboratory incubation experiment was conducted to examine the combined effects of chlorsulfuron and bensulfuron-methyl herbicides on the soil microbial biomass C (Cmic), N (Nmic) and their ratio in a loamy sand soil. The herbicides were added at four levels that were (C0B0) control, (C1B1) 0.01& 0.01, (C1B2) 0.01& 0.1 and (C1B3) 0.01&1.0 μg g–1 soil of chlorsulfuron and bensulfuron-methyl, respectively. The soil was then incubated in the dark at 25±1°C. Determinations of Cmic and Nmic were carried out at 1, 3, 5, 7, 10, 15, 25 and 45 days after herbicide application. The results showed that combined applications of herbicides have significant effect on soil microbial biomass C and N, particularly during the first 15 days of incubation, which declined after 25th day of incubation with C1B1 application rate. At 45th day of incubation, the effect of herbicides decreased significantly in C1B2 and it become non-significant as compared with the control. While, C1B3 was still found to be significant as compared to the control and C1B1 but it was at par with C1B2. The results also revealed that with C1B1 treatment the biomass C/N ratio was significantly higher within first 3 days of incubation as compared with the control. But with C1B2, the ratio was significantly different within first 5 days of incubation. While with C1B3 the ratio was found significantly higher within first 25 days of incubation as compared with the control. Increasing the application rate resulted in increased inhibitory effect on the soil microbial biomass and also combined addition of herbicides caused negatively more effect than their single application.