The acute (12 h) and chronic (7 or 14 d) effects of tributyltin chloride (TBT) on a new type of test fish, the Chinese rare minnow (Gobiocypris rarus), have been studied. High accumulation of the pollutant in the fish muscle and obvious changes in hepatosomatic index and gonad somatic index were observed after exposure. The ultrastructural findings show a series of pathological changes existing in the exposed gill cells and hepatocytes, which demonstrates the toxicity effects of tributyltin compounds on aquatic organisms. The results clearly show that the Chinese rare minnow is a new sensitive test fish material, whose exposure system is suitable for the extensive organometallic toxicity studies.