Abstract: Grass carp were exposed to 5 and 50 μg/L of diflubenzuron (DFB) and 1-(4-chlorophenyl)-3-(2-chlorobenoyl) urea (CCU) for 5 days. Water samples were analyzed for the parent compounds after 0, 6, 24, 48 and 72 h. Tanks without fish were used as controls. Water solubilities for DFB and CCU, measured by standard column extraction method, were 0.21 mg/L and 0.23mg/L respectively (Temp. 19℃±1℃). Lipid content of fish, determined by OECD method, 1987, was 1% (wet weight). HPLC was used for residue analysis of water and fish samples after they were purified. The results showed that, compared to DFB, CCU disappeared more rapidly from water both in control and in fish tanks. Meanwhile, its bioaccumulation value in fish was relatively low (BCF5<100), indicating a higher biodegradability in CCU than in DFB. The Bioaccumulation processes for both chemicals were related to their exposure concentration in water.