Objective The purpose of this study was to determine the restoring-capacity of a Chinese herbal medicine decoction to the ultrastructure of hepatocytes in eel with liver injury induced by Cu-exposure.Methods Eels Anguilla anguilla were injured with cupric sulfate and treated with a Chinese herbal medicine decoction mainly composed of Salvia miltiorrhiza,Schisandra chinensis(Turcz.)Baill and Radix Glycyrrhizae.At the end of the trial period,fish were killed,dissected and the liver was examined by electron microscopy.Results Compared with the control fish,the hepatocytes of Cupoisoned control fish showed mitochondria swelled with disintegration or disappearance of cristae,dilation,degranulation and disintegration of rough endoplasmic reticulum.Intracisternal sequestration,autophagosomes and vacuoles were often observed.Some nuclei of hepatocytes presented nuclear crenation.Compared with the Cu-poisoned control fish,the ultrastructure of hepatocytes of drug-treated fish showed recovery notably.Conclusion Our findings demonstrated that this Chinese herbal medicine decoction may promote the recovery of ultrastructure of hepatocytes in the copper-damaged eel liver,indicating an effective protective effect against those damages.