It has been reported that boron may be beneficial for optimal calcium metabolism and, thus, optimal bone metabolism. Therefore, we designed a study to determine the effect of boron supplementation on Ca and bone metabolism in rats. The rats of 80-l40g body weight were given a control(0ug), 5$mu extrm{g}$, 10$mu extrm{g}$, 20$mu extrm{g}$, 40$mu extrm{g}$, or 80$mu extrm{g}$ boron supplement per Is diet for 4-weeks. The results are summarized as follows. There were no differences in total food intake and weight gain among the experimental groups. fecal Ca excretion, urinary Ca excretion, apparent Ca absorption, Ca retention, serum alkaline phosphatase activity, and urinary hydroxyproline were not affected by boron supplementation. There was no difference in serum creatinine. Whereas, urinary creatinine excretion was increased with increasing boron supplementation, and conse-quently creatinine clearance was increased with boron supplementation. No differences were found in length, weight, density, Ca content of femur and scapular. The findings suggest that boron supplementation was not effective in Ca and bone metabolism in growing rats fed normal Ca diet. (Korean J Nutrition 31(6) : 1039-1048, 1998)