The heat capacity C-p,C-m of NpO2 was estimated for temperatures between 300 K and 1400 K. The C-p,C-m was evaluated as a sum of three terms, phonon vibration C-ph,C-m, dilation C-d,C-m, and Schottky specific heat C-s,C-m. The C-ph,C-m and C-d,C-m were calculated using the Debye temperature, Gruneisen constant and thermal expansion data obtained by high-temperature X-ray diffractometry. The coefficient of the linear thermal expansion (l.t.e.) for NPO2 was given as a polynomial function up to T = 1573 K. The estimated C-p,C-m was compared with that of previous studies. The present result at T = 300 K was 66.87 J . K-1 . mol(-1), which agreed well with previous results, 66.22 J . K-1 . mol(-1), measured by using calorimetry. The thermodynamic functions were given as a function of temperature.