Tan-Hsin Archive, an important first-hand research resource of Taiwan history, has some of its materials damaged by worm-eating or paper deterioration. To tackle this problem, the National Taiwan University (NTU) Library launched a systematic inventory and renovation project in 1990. This paper gives an account of the renovation work done at various stages, pinpoints problems in the preservation of this archive, introduces the guidelines for the mounting of the damaged documents in this collection, and concludes by proposing ways to preserve the repaired documents. Attempts will also be made to explore issues about the preservation of Tan-Hsin Archive in the future. The author hopes that the NTU Library's experience can be of some use to those institutions that hold archives so that together we can do something to improve the preservation of important national cultural heritage.