Objective To observe the effects of preservation period of blood samples on biochemical measurement. Methods By using automatic biochemical analyzer, the biochemical values of blood samples after different preservation periods were measured and analyzed. Results The biochemical values of blood samples after different preservation periods differed significantly. The values of TP, ALB and CHO were more sensitive to preservation periods. Conclusion It is important to unify the nreservation neriod of blood samnles during chronic toxicity testing studies.