The stability criteria are derived for a nuclear reactor with a power coefficient feedback. The power coefficient feedback is assumed to consist of two feedback paths, each with a single time constant. In reality, the system of the nuclear reactor is often well approximated by this model. The criteria are given in Table I and in Fig. 5, by which one can quickly determine the stability, when parameters are known. They also give an insight into the effects of various parameters on the stability of the nuclear reactor. The application of the criteria to a British-type gas-cooled reactor with a positive temperature coefficient of moderator is demonstrated. Comparisons are made with other works, of different approaches, on a fast reactor and a water-cooled reactor.