This paper is concerned with the study of the static pair correlation and the susceptibilities of ferromagnetics with spin 1/2 by the method of two-time Green's function of Bogolyubov and Tyablikov adopting the Heisenberg model. A marked difference is found in the behavior of these quantities for the systems with anisotropic and isotropic exchange interactions. In particular, for the case of the isotropic exchange interaction, the parallel susceptibility diverges below the Curie point down to the spin wave region. Consequently, the static spin pair correlation of the longitudinal component of spins shows the behavior with the distance which is different from that previously known. Due to the same cause, the susceptibility immediately above the Curie temperature deviates from the Curie-Weiss law.