The standard enthalpy of formation, low-temperature heat capacities, and enthalpy increments above 298 k were determined by the federal Bureau of Mines for synthetic dawsonite [naalco3(oh)2]. The enthalpy of formation was determined by hydrochloric acid solution calorimetry, with the result ahf deg. 298 = -469.4+-0.7 Kcal/mole. The low-temperature heat capacities were determined from 6 to 307 k by adiabatic calorimetry. Tabulated are low-temerature values of cp deg., S deg., and h.-H deg. 0 From 3 to 298 k. The derived entropy at 298 k is s deg. 298 = 31.55+-0.3 Cal/deg mole. Enthalpy increments above 298 k were obtained by copper-block drop calorimetry. Tabular data of cp deg., S deg., H deg.-H deg. 298,-(G deg.-H deg. 298)/T, ahf deg., Agf deg., and log kf are given from 298 to 477 k. Enthalpies and Gibbs energies of decomposition are also reported.