The protein content in rice grains is negatively correlated with eating quality. Protein content of the grains can be estimated using the normalized difference vegetation index (NDVI) with satellite or airborne sensor. The relationship between NDVI and panicle blast severity was examined to assess the effect of severity on the NDVI. As severity increased, NDVI estimated with both a radiometer and an airborne hyper-spectral sensor decreased. Severity of panicle blast must be assessed with the NDVI before estimating the protein of the grain.