It is very important for the disaster prevention to analyze the factors which influenced on the fluidityof debris flow. We investigated such factors in debris flows occurred around Higashi-Hiroshima in 1999. Weadopted equivalent coefficient of friction and dynamic coefficient of friction to evaluate the fluidity of thedebris flows. As the result of consideration with obtained data, the following things were elucidated: (1) Debrisflow which occurred in the torrent with larger catchment area tends to have large fluidity. (2) In case of eachtorrent, as debris flow moved downwards, dynamic coefficient of friction became smaller. (3) Debris flowstended to lose their fluidity at the places where there were trees, agricultural ponds and tortuosity of the channeletc. (4) The proportion of area occupied by trees is more suitable than the number density of trees as factorsinfluenced on the fluidity of the debris flow. When the proportion of area occupied by trees would becomegreater than some per mills, debris flows at such site could be controlled by the trees.