[Synopsis]In this paper, next subject is discussed. § 40. Magnetic properties of an imperfect electron gas. We discuss the effects of interparticle interaction affecting the magnetic properties of an electron gas. Two electrons prefer to be in an antisymmetric orbital wave function to minimize the repulsive energy. But in fermions, total wave function of two electrons with spin-1/2 must be antisymmetric. Therefore an antysimmetric orbital wave function requires a symmetric spin wave function. Thus the repulsive interaction would align the spins of the electrons. And the effect of a repulsive interaction enhances the paramagnetism. We here demonstrate this effect by considering an imperfect electron gas at very low temperature.