The relationship between the number of fecal pellet groups found in line transects and estimates of deer density based on block counts on Mt. Ohdaigahara in central Japan was examined and the validity of fecal pellet group counts for obtaining an index of sika deer population density was assessed. Sika deer population densities estimated by block count were 13.0/km² in spring, 18.3/km² in summer and 19.0/km² in autumn. Fecal pellet group counts showed low positive correlations with deer density in spring and autumn (0.69 in spring and 0.68 in autumn), but not in summer, indicating that deer density may not be predictable then. We suggest that fecal pellet group count reflects deer density in spring or autumn, and might be feasible as an index of deer population density.