To evaluate the spatial variation of nitrogen flux in urban-suburban catchments, topographic influenceson nitrate concentration, flux and runoff were examined at nineteen small catchments. The results indicatedno correlations between topographic parameters on one hand and NO3--N concentration, flux, and runoff,respectively. These results suggest that both of runoff and NO3--N concentration is controlled by factors such asland use and artificial factor. On the other hand, the fluctuation of NO3--N concentration decreases with increasein the catchment area. This means that we can estimate the common values of them in such catchment size.