We used the mechanical milling to prepare orthorhombic Sm0.12Ca0.88MnO3 samples with the average crystallite size (d) changing from 100 to 139 nm. Their magnetic and magnetocaloric properties were then studied upon magnetization data versus the temperature and magnetic field, M(T, H). The results revealed the samples undergoing the ferromagnetic-paramagnetic (FM-PM) phase transition at the Curie temperature TC ≈ 110 K. Around this transition, the magnetic-entropy change (ΔSm) reaches the maxima. The maximum |ΔSm| values are about 2–4 J·kg−1·K−1, corresponding to relative cooling power of 35–60 J·kg−1, for an applied field H = 30 kOe. The assessments based on Banerjee’s criteria and constructing a universal curve for |ΔSm(T, H)| data indicate the samples having the nature of a second-order phase transition. Also, the detailed analyses based on the Curie-Weiss law and magnetic-order exponent prove the existence of the Griffiths phase and magnetic inhomogeneity in the samples. These properties would be changed by changing d.

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