Root respiration was separated from total soil respiration in this study. Experiments were carried out in September 2003 at Yamashiro Experimental Forest located in Kyoto Prefecture. It is a secondary forest of broad-leaf trees including some conifer species. The root system was dug out and divided into several classes by size. The respiration rate of each size was measured by the closed-chamber method consisting of an IRGA, a pump, and a chamber made of acrylic. Temperature in the chamber was measured by thermo couple. The results showed that the smaller the diameter of the root was, the higher the respiration rate per unit weight was. A Mmuch higher rate was found in fine roots in comparison with other classes. From the relationships between basal diameter and root mass of each size for sample trees, root mass of each size per area was estimated. By combining the respiration rate and root mass of each size per area, root respiration could be calculated at 0.0707 mg CO2 m-2 s-1 as a total. More than the half was occupied by fine root respiration. Mean total soil respiration was 0.19 mg CO2 m-2 s-1 during this experiments. Therefore, the contribution of root respiration to soil respiration was estimated at 37.2%.