Although the importance of good conservation of historical sites including ancient royal tombs is well aware, still not much attention has been paid for facilities to realize it. There are numerous ancient royal tombs spread in Korean peninsula which are opened and some of them are selectively on display for public access. However, the conservation measures of these sites have not been seriously investigated. Even the level of understanding of the underground environment of tombs is not satisfactory. In the present study, we focus on the dehumidification loads to maintain appropriate conservation conditions in terms of temperature and humidity. Two experimental tombs different in size were built in KNU (Kongju National University) campus with the dimensions ($L{ imes}W{ imes}H$) of $1.0m{ imes}2.8m{ imes}1.0m;and;1.3m{ imes}3.0m{ ime}1.2m$, respectively, HVAC systems are installed to maintain a suitable condition for conservation, i.e., $22{pm}2^{circ}C$ in temperature and $55{pm}5%$ in relative humidity. The condensed water are measured to estimate the dehumidification loads while the temperature and the humidity inside the tombs were maintained within the specified range.