Relationship between diversity indexes of fishes and environmental factors were evaluated. In this study, a field investigation was carried out in a paddy-field area in the eastern part of Shimane Prefecture. Parameters of this study were water qualities, fishes, and physical environmental factors (water depth, flow velocity, vegetation coverage, soil coverage of undersurface and habitat space) in drainage canals. Eleven species of fishes were observed in the investigation sites and diversity indexes were calculated by Shannon-Wiener method. Factor analysis was conducted with the diversity indexes of fishes and the environmental factors. As a result, higher values of diversity index were found with lower concentrations of chemical oxygen demand (COD), total organic carbon (TOC), nitrogen and turbidity. In addition, the higher indexes were also found with slower flow velocity and higher levels of vegetation coverage, soil coverage of undersurface, habitat space and water depth.