Brown spot (BS) breakouts the third most common disease of Japanese rice crop. Normalized difference vegetation index (NDVI), which is calculated from spectral reflectance in red and near infrared band, is commonly used in remote sensing which has been put into practical use recently. It was suggested that the estimation of the amount of growth and protein content of brown rice with NDVI after heading stage in rice was inhibited under sever condition of BS. It was inferred that the reason of this was the correlation between NDVI and BS severity under sever condition of BS. There was the negative correlation between BS severity and spectral reflectance in near infrared band, though there wasn’t the correlation between BS severity and spectral reflectance in red band. Furthermore, spectral reflectance in near infrared band had correlation with BS severity under mild condition of BS. These results suggested that spectral reflectance in near infrared band was a promising index to monitor BS severity.