Abstract: The effects of Sodium arsenite on glucose-6-phosphate dehydrogenase (G-6-PDH) and lactate dehydrogenase (LDH) activities, RNA and protein contents in brain, gill, liver and muscle of Silurus lanzhouensis were investigated. The results indicated that during the 21d when the concentrations of Sodium arsenite were maintained safe in the water, G-6-PDH and LDH activities, RNA and protein contents decreased significantly in all tissues (P0.05). Then, remaining fish were transferred to clean water for the elimination phase of 21d. On the 21st day after moving, compared with the control level, G-6-PDH and LDH activities, RNA and protein contents in brain, gill, liver and muscle were restored to the control level (P0.05), except for the lower protein contents in brain and liver and higher G-6-PDH activity in liver (P0.05). These results suggested that arsenic could inhibit metabolic activity, induce RNA damage and the content of soluble protein, and this process was reversible after withdraw arsenic.