Liquid heat capacities of aqueous mixtures of diethanolamine (DEA) with 2-piperidineethanol (2-PE) were measured over the temperature range of 303.2 to 353.2 K with a differential scanning calorimeter. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the DEA + 2-PE + water systems were studied. For binary systems, heat capacities of the nine concentrations of DEA + 2-PE were also studied. A Redlich-Kister-type equation for representing excess molar heat capacity was applied to correlate the measured C-p of aqueous alkanolamine solutions. For a total of 176 data points for the DEA + 2-PE + water system, the overall average absolute percent deviation of the calculations were 10.6% and 0.1% for the excess molar heat capacity and the molar heat capacity, respectively. The beat capacities of aqueous mixtures of DEA with 2-PE presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.