Abstract: In order to study the metabolism and elimination of norfloxacin (NFX) in hybrid tilapias (Oreochromis aureusO.niloticus), single oral administration at dose of 20 mgkg-1 had been investigated in healthy tilapia at (252)℃.The result demonstrated: Plasma concentration-time datas of NFX were best fitted using a two-compartmental open model.Absorption, distribution and elimination half-life were 1.30,1.97 and 26.36 hours, respectively.The maximal plasma concentration was 0.546 gmL-1, peaking at 2.715 hour.Area under the plasma drug concentration-time curve was 14.491 ghmL-1.As an edible tissue, muscle was selected as target tissue in this experiment.The maximum residue limit (MRL) is 10 gkg-1 in muscle, the withdrawal time should not be less than 55 days under this experiment condition.