Since earthquake originating in the Nankai Trough is said to be inevitable in Japan, preparing for damages caused by a possible earthquake is an urgent issue. There were many cases in which the value of documents was impaired by biodegradation, such asadhesion of and stains on documents, as a result of the Great East Japan Earthquake on March 11, 2011. Since water characteristics in documents are heavily involved in the development of microorganisms, it is extremely important to know how to change water characteristics of paper and degrees of salinity when documents damaged by tsunami are salvaged. Unheard-of massive disaster occurred in the Sumatra-Andaman Earthquake in December 2004 and the Great East Japan Earthquake in March 2011 and the tsunami that followed both. But it has been reported that there was little mold growth although cultural properties and documents were put under a condition of high temperature and high relative humidity such as 35℃ and 83%r.h. for almost three months after the Sumatra-Andaman Earthquake. In this study, it was considered that measuring water potential of paper immersed in water or artificial seawater could reveal the ease for microorganisms to absorb water. In actual tsunami damage,the smaller the absolute value of water potential,the less pressure for microorganisms to absorb water from a substrate. Therefore, microorganisms can grow easily under such a condition. Assuming cultural properties and administrative documents damaged by seawater such as tsunami, paper samples were moistened with water or artificial seawater and water potential was measured to compare and analyze the difference. Data related with the ease of growth for microorganisms, such as kinds of paper and types of artificial seawater, are reported.