ABSTRACT: The Seljuk Tombs of the Seljuk Empire in the Ahlat region are included in UNESCO’s World Heritage Tentative List due to the fact that the tombstones are known to be the largest graveyards of Muslims with their historical significance. Tombstones were erected using ignimbrite type pyroclastic rocks which are widespread in the region, and several inscriptions and patterns were carved on them thanks to their softness and easy processing. However, these tombstones have been subjected to weathering effects for almost a duration of 800 years. The most striking point after the inspection of tombstones is that many of them were broken from the middle section. In this study, experimental studies were carried out on fresh ignimbrite specimens and particularly the effect of capillary water absorption on deterioration was investigated to reveal the factors leading to deterioration of Ahlat Seljuk tombstones. Accordingly, high porosity and capillary water absorption characteristics of the ignimbrites are found to be the major reasons for the deterioration of tombstones.