The detailed structural, magnetic, and cryogenic magneto-caloric properties of chromium-substituted gadolinium iron garnet (Gd3Fe5-xCrxO12) nanocrystalline powders were studied using the facile autocombustion method and a calcination temperature of 1100 °C. The X-ray diffraction pattern showed that all samples were single-phase with cubic Ia3d symmetry. The temperature and field-dependent magnetization data of Gd3Fe5-xCrxO12 samples revealed a ferrimagnetic ordering at low temperatures. Upon Cr3+ substitution, the Curie temperature reduced by 7% at x = 0.25 from 560 K for x = 0.00 sample. In a field up to 5 T, the maximum magnetic entropy change was observed as ΔSM ∼ 3.8 J K−1 kg−1 for x = 0.00 and −ΔSM ∼ 3.9 J K−1 kg−1 for x = 0.25 sample, while the maximum relative cooling power, RCP, value of 420 J kg−1 was measured for x = 0.25 sample, which is 10% larger than the x = 0.00 (RCP ∼ 380 J kg−1). Therefore, Cr3+ substituted Gd3Fe5-xCrxO12 samples exhibit promising magneto-caloric performance and have potential low-temperature magnetic refrigeration applications.