A method for calculating the temperature coefficient of the neutron multiplication factor in an infinite homogeneous medium is investigated for the purpose of discussion of the temperature coefficient for thermal reactors. Two kinds of expression for the temperature coefficient of the neutron multiplication factor are derived and given in terms of solutions of the integral equations which describe neutron balance in a stationary homogeneous system. The results of numerical calculations performed with the exact formula derived are compared with those based on the Maxwellian distribution model. The present method is recommended for accurate calculation, particularly in the case of strong non-1/v cross sections. For the case of weak non-1v cross sections, the Maxwellian distribution approximation suffices for obtaining fairly good results.