Image quality from electronic endoscopes is poor compared with that from conventional optical endoscopes that use color film. Our goal is to improve the image quality, particularly the color reproduction of electronic endoscopes. To achieve our goal, we have developed the endoscopic spectrophotometer to measure the spectral reflectance of gatric mucous membranes. Three hundred and ten spectra have been analyzed by principal component analysis. The results indicate that the reflectance spectra can be adequately described using only three principal components. Based on the above experimental result, we show that the spectral reflectance of gastric mucous membranes can be calculated from the R, G, B signals of conventional electronic endoscopes. Therefore, spectral reflectance of all pixels in gastric mucous membranes taken by electronic endoscopes can be estimated within less than the average color difference ΔE_uv^* = 2.66 in the L*u*v* color space. Computer simulations of the color reproduction of electronic endoscopes were performed, and the resulting spectral characteristics under various illuminants are described and analyzed.