Ectomycorrhizal (ECM) fungi are major symbiotic microorganisms with the roots of many forest tree species and play an important role in forest carbon cycling. In estimation of the role of ECM fungi in forest carbon cycling, fungal content of ECM tips is an important parameter. Therefore, I investigated the proportion of fungal content of ECM tips and discussed about factors affecting them. ECM tip samples were collected from subalpine and temperate forests in Japan. The proportion of fungal content of ECM tips was estimated by three methods. The proportion of fungal content of ECM tips ranged from 18-84%, and these values differed among tree species and fungal species. My finding suggested that it is necessary to consider tree species composition as well as fungal species composition in each forest ecosystem, when using the fungal content of ECM tips in the estimation of forest carbon dynamics.