Abstract: The nitrite conservation time of formalin fixed liver and kidney were investigated. 40 male rats had been divided into 4 groups with nitrite oral doses of 110(LD50),220 (LD) and 450 (over LD100) mg/kg respectively.Each rat liver and kidney(the survivors were sacrificed) was divided into two parts: formalin fixed and non-formalin fixed.As a result, the conservation time was prolonged remarkablely in the formalin fixed part.Nitrites could be detected as long as three months in all administrated groups while in non-formalin fixed part, 20 days at the longest (450 mg/kg group) .It shows a great adventage in the work of identification in the field of forensic medicine as it is ordinary to get the samples of cases fixed with formalin.