Objective To systematically investigate the effects of Dangmu extract syrup on the growth and development of 4-day-old (postnatal day 4,PND4 ) Sprague-Dawley (SD) rats and its toxic reactions. Methods According to the whole litter design method, 128 young mice (PND2 ) were randomly divided into negative control group and low, medium and high dose groups. From PND4 , the animals were orally given pure water, 31 g/kg, 93 g/kg and 280 g/kg (calculated as raw herb material) of Dangmu extract syrup, respectively, once daily for 18 consecutive days, with a 15 d of recovery phase. During the study period, the general state, growth and development, nerve reflex function, spontaneous behavior, hematology, coagulation, blood biochemistry, immune function, growth hormone and histopathology of the animals in each group were observed or examined. Results After 18 d of continuous administration, compared with the negative control group, GLU (male and female) in the medium and high dose groups increased (P<0.05 or P<0.01), LDH (male and female) and AST (male) in the medium and high dose groups, ALT, AST (female) in the high dose group decreased (P<0.05 or P<0.01), RET and percentage of RET (male and female) in the low and high dose groups, RET (male) in the medium dose group increased (P<0.05 or P<0.01), spleen mass and the organ-to-body mass ratio (male and female) in the low and high dose groups and female in the medium dose group increased (P<0.05 or P<0.01). Splenic nodule structures were formed in all dose groups with large size and number, and there was a dose relationship in the degree of changes. After 15 d recovery period, compared with the negative control group, GLU (female) in the low dose group increased (P<0.05), ALT, AST, ALP, TG (female) in the medium and high dose groups, GGT, TG, TCHO (male) in the medium dose groups, AST, ALP, TG, LDH (male) in the high dose group decreased (P<0.05 or P<0.01), RET (female) and percentage of RET (male) in the high dose group increased (P<0.05). compared with the 18 d of continuous administration, the spleen structures of the animals in each group were more completely developed and the splenic nodule structures were obvious, but no significant difference was noted in the comparison between groups. No significant drug-related changes were observed in other test result. Conclusions Dangmu extract syrup advanced the development of complete spleen structure in 4-day-old SD rats, accompanied by the enhancement of its hematopoietic function, and at the same time, it caused the animals, blood glucose to rise, the enhancement of glucose metabolism function led to the increase of related enzyme consumption, and led to the decrease of some liver function parameters, and showed a dose correlation. There was no gender difference in the changes, which were reversible after stop administration, and the mechanism of the changes needs to be further explored and confirmed. In the clinical trials, attention should be paid to the control of the dose of the test article, and regular monitoring of the spleen and related blood and clinical chemistry parameters.