In order to identify effective hepatoprotective herbs for clinical application in fish farming, 200 mg/kg olaquindox (OLA) was added to a basal diet (group 1, control) to form OLA diet (group 2), then 1.35, 2.7 and 5.4 % (w/w) of a Chinese herbal formulation, Yingchen decoction (YCD), were added to the OLA diet to form three additional diets for groups 3, 4 and 5, respectively. A total of 375 juvenile Jian carp (Cyprinus carpio var. Jian) (52.12 ± 2.95 g/tail) were divided into five groups (triplicates per group) and fed the five diets mentioned above, respectively, for 6 weeks. At the termination of feeding experiment, serum biochemical indexes, viability of hepatocytes and the hepatopancreas microstructure for each group were detected and observed. The results showed that serum ALT and AST in group 2 were significantly higher than the control (P < 0.05). Plasma membranes hepatocyte nuclei in group 2 were found to be mostly indistinct, compared to group 1, and gradually recovered with the increasing supplementation of YCD in group 3, 4 and 5. The viability of isolated hepatocytes in group 2 was the lowest and gradually recovered with the increasing supplementation of YCD in group 3, 4 and 5. The results suggest that YCD protected the Jian carp hepatopancreas against injury from OLA, and that 5.4 % YCD would be the optimum dosage in a Jian carp diet.