Effects of pH, sizing agent, and starch on the natural deterioration of 45 printed wood-free papers stored 1-32 years was investigated in terms of MIT folding endurance, brightness, and L*a*b* values. The neutral and alkaline papers retained their folding endurances well and significantly lost their yellow color (b*) during storage. The folding endurance of the acidic papers stored more than 15 years showed a declining trend with increased storage time. The sizing agent content in the papers stored more than 10 years increased and the amount of starch decreased with increasing storage years. A larger amount of the sizing agents correlated with less folding endurance and more yellow color of the papers. The relation between the starch content and the degree of yellow color of the papers was unclear, and the endurance of the papers increased with the increase in starch content.