The purpose of this study was to investigate the effect of training age on bone mineral density (BMD) of male martial arts participants. Martial arts training involves intense muscular contractions and compressive forces, both of which have been shown to effectively stimulate bone formation. Subjects were divided into three groups. The first group (n = 9) started their martial arts training in their early teens (during puberty) an continued for a period of at least five years. The second group (n = 13) started their martial arts training after age 18 (after puberty) and continued for a period of at least five years. Both groups trained between two and three times per week. The control group (n = 9) consisted of individuals of ages similar to the martial artists, with no martial arts training. BMD was measured at the hip, spine, and right and left femur using dual energy X-ray absorptiometry (DEXA). Body composition was also obtained for each subject. Significant differences were found in the percent body fat and total fat weight between the early training age group and the later training age group, and in the right and left femoral neck BMD values; with the early training age group having significantly higher values than both the later training age group and the controls. Based on these results, it is probable that martial arts training at a young age positively effects bone mineral density values.