Abstract: The distribution and depletion rules of MG and its metabolite LMG in channel catfish was investigated after bath treatment of 7 mg/L MG. Channel catfish were raised in the cages in the pool. Blood, muscle, liver, skin and kidney of channel catfish were analyzed by HPLC/MS/MS. The data of drug concentration-time were analyzed using pharmacokinetics software 3p97. The results showed that blood concentration-time data of MG and LMG were both best fitted using a two-compartment model with first absorption. The pharmacokinetic equations were CMG =683.063 e-0.248t+11.176 e-0.006t- 694.239 e-0.333t and CLMG =757.240 e-0.222t +14.474 e-0.007t 771.714 e-0.382t. Peak concentrations of MG and LMG were 81.560 ng/mL and 159.619 ng/mL at 3.480h and 3.623h, respectively. The distribution volume (Vd/F) of MG and LMG were 37.689 L/kg and 21.125 L/kg, respectively. First-order rate constants for MG and LMG distribution phases () were 0.248/h and 0.222/h, respectively, First-order rate constants for MG and LMG elimination phases () were 0.006/h and 0.007/h respectively. The absorption half-life T(1/2) were 2.794h and 3.124h, respectively. The elimination half-life T(1/2) were 113.068h and 105.841h respectively. First-order rate constants for MG and LMG distributions from central compartment to peripheral compartment (K12) were 0.020/h and 0.015/h respectively. First-order rate constants for MG and LMG distributions from peripheral compartment to central compartment (K21) were 0.159/h and 0.121/h, respectively. The areas under the curve (AUC) were 2493.944 ngh/mL and 3601.863 ngh/mL. The results of MG and LMG concentrations in muscle, skin, liver and kidney of channel catfish showed that the orders of 4 kinds of tissues concentration levels of MG from high to low were skin, muscle, kidney and liver. MG was easy to accumulate in skin, and residue time was the longest. Because MG was metabolited by liver fastly, low concentrations of MG were determined in liver. The Elimination equations of MG in muscle, skin, liver and kidney were C=5.570 e-0.009t, C=6.302 e-0.007t, C=4.791 e-0.006t and C=4.591 e-0.002t. Those correlation coefficients (r2) were 0.773 respectively. The elimination half-life (T1/2) of MG in muscle, skin, liver and kidney were 3.2d, 4.1d, 4.8d and 14.4d, respectively. MG was not detected in muscle, skin, liver and kidney of channel catfish at 45d, 60d, 30d and 60d respectively. The orders of 4 kinds of tissues concentration levels of LMG from high to low were liver, skin, muscle kidney. The tissue with the longest residue time of LMG was also skin. The Elimination equations of LMG in muscle, skin, liver and kidney were C=6.491 e-0.004t, C=6.958 e-0.003t, C=6.722 e-0.007t, and C=6.162 e-0.002t, repectively. The correlation coefficients (r2) of them were 0.673. The elimination half-life of MG in muscle, skin, liver and kidney were 7.2d, 9.6d, 4.1d and 14.4d. LMG was not detected in muscle, skin, liver and kidney of channel catfish at 90d, 90d, 60d and 90d, respectively. MG and LMG were not detected at 90d and the average water temperature was 26.4℃ during the experiment from May 17, 2011 to July 15, 2011. Malachite green and its metabolite Leucomalachite green should at least through 2376℃d to eliminate at 7 mg/L malachite green for 2 age of channel catfish.