Florfenicol(FFC),a synthetic broad-spectrum antibiotic,with a structural analogue of thiamphenicol is active against many thiamphenicol-resistant strains. Due to its broad antibacterial spectrum and with no side effects of aplastic anemia, FFC has been widely used in livestock,poultry,and is also legally permissive to be used in aquaculture. To study the absorption characteristics of florfenicol in GIFT Nile tilapia, which was the biggest quantity export farming fish, the 10 hour blood samples were detected using high-performance liquid chromatography with fluorescence detection method after feed administration of 0,5,12,20,40,80,100 mg/kg of florfenicol at 30℃.Results showed:the concentration was (Mean±Standard Deviation,n≥6) 0,1.49±0.46,2.66±0.62,5.08±0.75,10.60±2.34, 13.74±2.87 and 14.42±0.49 μg/mL respectively. The concentration increased with the increase of dosage at the same time in blood,while the increase amplitude decreased, which indicated the decreased utilization of drug to the increasing dosage. In the same experiment condition, 0 (control), 12,20,40,100 mg/kg body weight of florfenicol a day were given to GIFT in feed for 7 consecutive days to study the histological toxicology of florfenicol.There were no mortalities or clinically observable changes found at any of the dose levels tested. Dose dependent ultrastructural damages were found in cells of kidney and liver at the dosages of 40 and 100 mg/kg,the damage could not be repaired after 7 days at the end of the test, while no obvious pathological changes were found at dosages under 20 mg/kg. We recommend the dosage of no more than 20 mg/kg, otherwise it may damage the function of liver and kidney,lower utiliztion and cause environmental pollution, etc.