Acidic sulfates such as aluminum sulfates and ferric sulfates are often observed on the wall of tuff or volcanic rocks in Japan. We investigated wall surfaces of an artificial cave dug from 1941 to 1945 in the Miocene tuff. The cave locates in the historic site of Yoshimi Hyaku-Ana which is ancient graves of 6-7 centuries. The cave was suffering from severe salt efflorescence and deterioration of its cause. Salts are much in dry winter but less in humid summer. We set up twelve investigation points for monthly monitoring of temperature and humidity. Fallen salts and debris at each point were also collected monthly from November 2008 to December 2009. Main salt minerals, detected by XRD, are hard and granularly effloresced alunogen (Al2(SO4)3.17H2O) on the walls near the entrances, and gypsum was found on the inside walls in the humid summer. On the contrary, powdery effloresced halotrichite (FeAl2(SO4)4.22H2O), sodiumalum (NaAl(SO4)2.12H2O) and epsomite (MgSO4.7H2O) were detected in the dry winter. Jarosite (KFe3(SO4)4.(OH)8) minerals were observed on iron hydroxide stains on the walls in every season. Halotrichite, sodiumalum and epsomite damaged the walls most severely especially in the dry winter. The amount of salts and debris from the inner wall were greater than those from near entrances.