The main purpose of this study was to investigate anthropometry and body composition in 26 male ultramountain runners who participated in Trans Japan Alps Race 2014, a multi-stage ultramountain running race over 415 km to be covered within 5-8 days. The second purpose was to investigate the changes in skinfold thickness during the race. Before the race, all participants were examined in terms of body weight, BMI, skinfold thickness at 8 sites and estimated percentage body fat. In addition, the finishers (n=14) were re-examined in the post-race period. The main findings are summarized below. 1. The participants had a mean (±SD) body weight of 62.3±5.1 kg, a BMI of 21.5±1.4 kg/m², a sum of 8 skinfold thickness of 57.7±15.5 mm, and an estimated percentage body fat of 12.0±2.4%. There were no significant differences in any parameters between the finishers and the non-finishers. 2. The sum of 8 skinfold thickness in the finishers was significantly reduced by 11.3% after the race (Pre : 55.0±13.6 mm, Post : 48.8±12.1 mm), representing a dramatic response in comparison with a previous study that investigated ultramarathon runners in a 100-km ultramarathon race (0.9%).