The concentration and δ^<15>N value of nitrate nitrogen (NO_3-N) of spring waters in Tamagawa basin were measured from June 1995 to January 1999. 1) Nitrate nitrogen concentrations and δ^<15>N values of the spring waters were 0.12 to 14.1 mg L^<-1> and +0.53 to +8.75‰, respectively. 2) Both were low in the spring waters that flowed from the upper layer of the Tama terrace in the left side of the upper stream of the Tamagawa River, while δ^<15>N values were high with different concentrations of NO_3-N from the lower layer. 3) The NO_3-N concentrations and δ^<15>N values in the spring waters from the lower layer of the Tama terrace in both sides of the central stream of the Tamagawa River were higher than those of the upper stream, reflecting human and agricultural activities. 4) The spring water passing through reed plants have decreased NO_3-N concentration and increased δ^<15>N value.
