Using 168 female Sprague-Dawley rats, we determined whether the peak bone mass could be increased, and which drugs would be effective in suppressing the rate of decrease in bone mass by continuous administration from childhood. At the age of 3 months, these 168 rats were divided into five groups depending on the type of diet that they were fed (control, regular; group A, vitamin K2; group B, vitamin D; group C, high calcium; group D, vitamins D and K2 and high calcium) and kept to the age of 16 months. Dual-energy X-ray absorptiometry (DXA) was used to measure the bone mineral density of the femoral epiphysis and microcomputed tomography (CT) to analyze its fine structure. The average bone mass increased rapidly with age and reached a peak at the age of 8 months. Peak bone mass for the four drug administration groups was higher than that for the control group. Among these four groups, the peak bone mass was the highest in group C and the rate of decrease the smallest in group D. The results of the present animal study suggest that the peak bone mass of humans can be raised by consuming sufficient amounts of vitamins K2 and D and calcium continuously from childhood, and that this diet will suppress the rate of decrease in bone mass, thus ultimately preventing bone fractures caused by osteoporosis.