pH, O₂, ammonia and nitrate concentration profiles contained in the attached biofilm on river rocks were measured with microelectrodes. The photosynthesis under the bright lux condition (8000lux) promoted the rapid O₂ concentration increase on the surface of the biofilm. Ammonia consumption activity under the bright lux condition was about twice as much active as under the dark lux condition. As for the attached biofilm on the riverbed rocks obtained from 5 spots in Shimanto river basin, ammonia consumption activity of the rock collected from the upstream was 0.06-0.13μmol/cm²⋅h, which showed more active value than that of the downstream.