This study was performed to investigate the effect of co-existence of carbofuran and chlorothalonil on the short-term bioconcentration factor in Brachydanio rerio(zebrafish). The fishes were exposed to the single and combined treatment of carbofuran and chlorothalonil for 1, 3 and 5 days. Experimental concentrations of carbofuran were 0.05 and 0.10 ppm under the single treatment. And those of chlorothalonil were 0.005 and 0.010 ppm. Experimental concentrations of the combined treatment of carbofuran and chlorothalonil were 0.05 ppm+0.005 ppm, 0.05 ppm+0.010 ppm, 0.10 ppm+0.005 ppm for 1, 3 and 5 days, respectively. Carbofuran and chlorothalonil in fish and in test water were extracted with n-hexane and acetonitrile. GC-ECD was used to detect and quantitate carbofuran and chlorothalonil. 1-day, 3-day and 5-day bioconcentration factors(BCF$_1$, BCF$_3$ and BCF$_5$) of each pesticide were obtained from the quantitation results. The depuration rate of each pesticide was determined over the 24-h period after combined treatment. The results were as follows: Carbofuran did not bioaccumulate in zebrafish under the single and combined treatment for testing periods. BCF$_1$ values of chlorothalonil in concentration of 0.005 and 0.010 ppm under the single treatment were 0.508, 0.621, BCF$_3$ were 1.327, 1.511 and BCF$_5$ were 1.331, 1.597, respectively. BCF$_1$ values of chlorothalonil were 0.512, 0.520 and 0.619, respectively, when the concentration of carbofuran and chlorothalonil in combined treatment were 0.05+0.005, 0.05+0.010 and 0.10+0.005 ppm. BCF$_3$ values of chlorothalonil 1.341, 1.338 and 1.513, respectively, and BCF$_5$ values of chlorothalonil were 1.332, 1.327 and 1.521, respectively, under the above combined treatment. Depuration rate constants of chlorothalonil in concentration of 0.005 and 0.010 ppm under the single treatment were 0.011 and 0.012. Depuration rate constants of chlorothalonil were 0.011, 0.010 and 0.011, when the concentration of carbofuran and chlorothalonil in combined treatment were 0.05+0.005, 0.05+0.010 and 0.10+0.005 ppm. It was observed that no significant difference of carbofuran and chlorothalonil concentration in fish extracts, test water, BCFs and depuration rate constants of carbofuran and chlorothalonil between combined treatment and single treatment. It was considered that no appreciable interaction at experimental concentrations due to lower concentrations than LC$_{50}$. It is suggested that the difference of BCFs between carbofuran and chlorothalonil due to those of fat composition of fish and solubility of carbofuran and chlorothaionil.