Abstract: Spectral transmittances in wavelength ranged from 300 to 1100 nm of rice and cucumber leaves treated with culture solution in five different nitrogen levels were measured in this study. The correlated relationships between the above spectral transmittances and their chlorophyll contents and nitrogen contents indicated that the 560, 650, and 720 nm as feature wavelength and 940 nm as reference wavelength were useful for plant nutrient diagnosis. Correlation analysis and their regression examination between 21 spectral feature parameters composed by the transmittances at above wavelength, and the leaf chlorophyll contents and nitrogen contents showed that spectral feature parameters of (T940-T560)/(T940+T560), log(T940/T560) and log(T940/T650) were available for plant nutrient diagnosis with less than 8% relative error in measurement tests of rice and cucumber leaves. Therefore, the above spectral feature parameters as plant nitrogen indices can be used to estimate the chlorophyll content and nitrogen content and thus support for nondestructive plant nutrient detection.