Applying economically optimal N rate (EONR) is suggested to have both economic and environmental benefits. Accurate techniques for diagnosing EONR for winter wheat are not well developed. Our objective was to predict EONR for winter wheat using a spectral radiometer. Five experiments using a complete factorial design with four replications were conducted from 1998 to 2004 in Missouri. Reflectance was measured at Feekes growth stages 3 and 5 at eight wavelengths from 510 to 830nm. The EONR for N applied at Feekes 5 was determined from modeled yield response to N. The relationship between reflectance and EONR will be determined and discussed.