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Cobaltites show intriguing magnetic and transport properties, when compared with manganites for instance, as they exhibit an additional degree of freedom: the spin state of the Co ions. For Nd 0.5 Sr 0.5 CoO 3 this spin conguration is not well-established, as well as the magnetic ordering below the Curie temperature. Thus, in the present eort, magnetization measurements and a mean-eld theoretical model were developed in order to understand in detail these aspects of the half-doped Nd 0.5 Sr 0.5 CoO 3 cobaltite. These results show that the Co and Nd magnetic sub-lattices couple antiferromagnetically below Curie temperature T c =215 K down to very low temperature. These ndings clarify the presence of the plateau observed at 80 K on M(T) curve, which is erroneously attributed, in the literature, to the onset of an antiferromagnetic ordering. Magnetization data also clearly shows that Co 3+ and Co 4+ are in an intermediate spin state. In addition, experimental and theoretical magnetic entropy change were determined and a comparative analysis among these two leads to ratify the results above claimed. Finally, from all those results, a magnetic phase diagram for Nd 0.5 Sr 0.5 CoO 3 could be drawn.