The ideal gas thermodynamic properties (Cp0, S0, H0−H00, (H0−H00)/T, −(G′−H00)/T,ΔHf0, ΔGf0, and log Kf) for propanone and 2-butanone in the temperature range 0 to 1500 K and at 1 atm were calculated by statistical mechanical procedures, using rigid-rotor and harmonic-oscillator approximations. The internal rotation contributions to thermodynamic properties were evaluated by use of a partition function formed by summation of internal rotation energy levels. The calculated heat capacities and entropies are in agreement with the available experimental values.