The authors examine the effect of higher relative humidity (79% RH) on the deterioration of silk fabrics. Silk fabrics were dyed with three kinds of vegetable dye, such as <i>Sikon</i>, <i>Suô</i>, and <i>Kariyasu</i>. These samples were exposed in oxygen at a (RH 79%, 20-30°C, for 80 or 160 days) or were irradiated by ultraviolet (UV) light (Ushio Denki Co., Xenon lamp UXL-500D, Main wavelength=365-370 nm, Illumination intensity = 15-16 microampere. Tensile strength, elongation to break, and Young's modulus of the samples were measured. Elongation of the sample was caused by the iron mordant, decreased by about half value by the increase of RH from 30-50% to 79%. The amount of metal eluted during aging treatment and the discoloration were also measured. But the remaining results were almost the same in the lower RH conditions (reported in a previous paper).