In order to better conserve, protect and use paper documents and lengthen their lifespans, we reviewed the influences of acid-base properties of paper, relative humidity, temperature, light, air contaminants and microorganism on the aging of paper, and the mechanisms and effectiveness of mitigation measures. The acid-base property of paper has a great influence on its aging:the more acidic the paper is, the quicker the aging will be. Therefore, paper documents should avoid exposure to acidic materials, and severely acidified ones should be de-acidified. Relative humidity has a two-way influence on paper aging. The aging of paper becomes quicker with the increase of relative humidity. However, physical damage, such as embrittlement and warp, will occur to paper when the relative humidity is too low. Furthermore, fluctuation of relative humidity is more harmful than undesirable values. The optimum relative humidity range for paper document conservation is 40%~60% where steady values are easy to reach and maintain all year round. The rate of aging of paper also increases with the rise of temperature. The optimum temperature for paper document conservation is around 20℃. In addition, fluctuation of temperature will cause variation of relative humidity, and therefore temperature stabilization is also important. The aging of paper can be severely accelerated by light, and the damage can accumulate. Ultraviolet rays can cause the strongest damage to paper, while infrared rays can induce heat effects. Therefore, paper documents have to be kept out of sunlight. Lamps with ultraviolet or infrared rays should not be used for illumination and the exposure period be minimized as much as possible. Air contaminants, mainly acetic acid, formic acid and 2pentyfuran, may accelerate the aging of paper, so air in storage rooms should be kept clean and storage container be ventilated. Mold may also accelerate the aging of paper and discolor it, so disinfection of paper documents must be done before being put in a library.