The magnetic phase transition and magnetic entropy change (−Δ S M ) in the La 0.40Nd 0.30Sr 0.30Mn 0.70Cr 0.30O 3 perovskite were investigated by measuring the magnetization as a function of temperature. The ferromagnetic transition temperature T C and the critical exponents β and γ, determined by analyzing the Arrott plots, are found to be T C = 191 K, β = 0.433, γ = 1.053 and δ = 3.486. These values for the critical exponents are close to the mean-field values. In order to estimate the spontaneous magnetization M s ( T) at a given temperature, we use a process based on the analysis, in the mean-field theory, of the magnetic entropy change (−Δ S M ) versus the magnetization data. An excellent agreement is found between the spontaneous magnetization determined from the entropy change ((−Δ S M ) vs. M 2) and the classical extrapolation from the Arrott curves ( μ 0 H/ M vs. M 2), thus confirming that the magnetic entropy is a valid approach to estimate the spontaneous magnetization in this system and in other compounds as well.