Various kinds of waste paper with different ash content were solubilized by hot compressed water (HCW) in mini-batch reactor. When the operating conditions of reaction temperature and time were varied, it was found formic, acetic and lactic acids were mainly produced. Waste paper with higher calcium carbonate content was favorable in producing much more amount of organic acids. When a flier, 26.8wt% ash content and 10wt calcium carbonate content, was treated under the condition of 275ºC and 30min, the conversion rate of water-solubilized carbon of about 33wt% and acetic acid of 42mg/g-waste paper were obtained.