Abstract The potentialities of ac calorimetey are investigated experimentally and theoretically. The effects of the sample-holder and of the heat-leakage into the wires on the measured temperature-oscillations are discussed. It is shown that the effects can lead to incorrect measurements. A proper choice of materials and external parameters enables the construction of the calorimeter with sensitivity of about 10 −8 J/K at 5K. The presented calorimeter gives an opportunity to measure the heat-capacity temperature dependencies in the steady-state mode with a resolution of about 0.01K in the range 1–300K.