Objective To observe the effects of pentobarbital sodium,chloraldurat and ethylcarbamate on hematology in male SD rats. Method Male Sprague-Dawley (SD) rats were anesthetized by intraperitoneal injection of pentobarbital sodium, chloraldurat and ethylcarbamate, respectively. Serum biochemical parameters and blood cell indexes were determined within 20 minutes after injection. Results Some blood biochemical parameters and blood cell indexes of anesthetized rats showed significant difference in comparison with normal rats. Conclusion Anaesthesia can affect the hematology considerably. Therefore, scientific researchers should select anaesthetics properly.