Abstract The Green's function method is applied to the study of isotropic antiferromagnetism for the case S≥1/2. Expressions are obtained for the energy of the ground state, the sublattice spontaneous magnetization, and the parallel susceptibility. These results are compared with those of the spin wave theory for low temperatures. For high temperatures they are found in agreement with the well known results of other theories. Thus, the present theory gives a unified result which is approximately valid in the whole temperature range.