Thirty-three pieces of modern hand-made Japanese paper and a piece of Chinese paper were tested for their M.I.T. folding endurance and the pH of cold water extracts before and after accelerated aging at 80°C and at a relative humidity of 65% for 56 days. In general, folding endurance retained after accelerated aging is positively correlated to the pH of cold water extracts. Bleached specimens are more easily deteriorated than unbleached ones after the aging.