The aim of this study is to present an evaluation of the thermal load effects on the behavior of a concrete arch dam in Thailand. A Three-Dimensional Finite Element model for the thermal transient analysis was implemented to determine the thermal distribution in the dam body. Environmental conditions, such as reservoir water temperature at all depths, ambient temperature, and solar radiation were considered in the analysis. Then, structural analysis was conducted to evaluate deflections and stresses in the dam caused by the temperature profile. The thermal analysis results indicated that the upstream face is strongly affected by reservoir water temperature, while air temperature and sunlight mostly affect the downstream and crest faces. The solar radiation increases the concrete surface temperature by about 2 ℃ to 7 ℃ above the ambient temperature and causes nonuniform temperature distributions on the dam faces. Though prior literature shows significant effects of seasonal temperature variations on dam behavior, the structural analysis results in this paper show that the thermal loads contribute very little to the stresses and deflections of a dam in Thailand.