Full width at half-maximum (fwhm), peak and integrated reflectivities of (111) reflection curves from curved silicon crystals were determined at various radii of curvature between 1m and infinity. The double crystal arrangement of (n, -n) setting was used with Cukα radiation. Angles between the surface and the diffracting lattice plane were 0° in one specimen and 6.9° in the other. The fwhm, peak and integrated reflectivities were almost equal to those of perfect crystals when the radius of curvature was larger than 10m and 20m for symmetrically and asymmetrically cut crystals, respectively. This suggests that these three quantities for a flat perfect crystal can be used in estimating X-ray optical performances of curved crystal monochromator for synchrotron radiation because the radius of curvature is usually a few tens meter.