Ash content is one of matters of concern in a viewpoint of breeding programme for Japanese home-grown wheat. A near-infrared diffuse reflectance (NIR) technique was applide to determination of ash in 60% extraction flours from 2 varieties of the wheat. A distinct tendency that flour of a finer particle size has a higher ash content was observed in the NIR spectrum, resulting in an unstable property of diffuse reflectance which was affected by mutural interaction of moisture in the flour with its flour particle. As a result of calibrations performed, the most accurate calibration was obtained with a multiple linear regression analysis using second derivative of absorbances at 4 specific wavelengths involving an absorbance at 2344nm which was assigend to a bran-related substance in the flour. It is possible to determine ash indirectly in connection with an inclusion of the branrelated fraction in the flour. However, prediction of ash in "unknown" wheat flours from different varieties from those used for performing the calibration resulted in serious errors on account of a bias effect between the varieties.