Although it has traditionally known that deer antler and medicinal herbs extract contain some functional components for health promotion, the nutritional significance remains to be elucidated. This study examined the efficacy of deer antler extract (DA) , medicinal herbs extract (MH) and their mixture (DAMH) on serum IGF-I, bone growth with growing rats in vivo and splenocyte proliferation with spleen cells in vitro. Three week-old young female rats (Sprague-Dawley) were divided into 4 groups and then fed basal diet (AIN-93G) or experimental diets containing DA, MH, DAMH, respectively, for 7 weeks. We collected blood, liver, kidney, spleen, femur and tibia from rats. There was no significant difference in weight gain, but food intake increased in DA- and MH-fed groups. There were no signs of liver and kidney damage in the DA, MH and DAMH-fed groups compared to basal diet group. In femur and tibia, wet weights: breaking forces and bone minerals (Ca, Mg and Zn) were significantly higher in the DA-fed group than in the other groups. Serum alkaline phosphatase (ALP) , bone-specific alkaline phosphatase (BALP) activities were significantly lower in the DA, MH, DAMH-fed groups than in basal diet group. Also, serum insulin-like growth factor-I (IGF-I) concentrations were significantly increased in DA-fed group compared to the other groups. Therefore DA was shown to have an activity of bone growth promotion by increasing the IGF-I, a major bone growth factor. The deer antler extract showed an enhanced immune action on the primary cultured-cells from spleen of rats, representing that splenocytes were proliferated by lipopolysaccharide (LPS), but not by concanavalin A (Con A). These results indicate that deer antler extract has beneficial effects on bone growth via IGF-I and on splenocyte activation.