Structural characteristics and magnetocaloric effect of Sm2NiMnO6 double perovskite oxide nanoparticles synthesized via the solution combustion technique have been investigated. From the X-ray structural study, it is found that the Sm2NiMnO6 compound crystallizes in the monoclinic structure (P21/n space group), where Ni and Mn atoms are ordered at 2c and 2d sites, respectively. Transmission electron microscopic image reveals agglomerated nanoparticles with an average particle size of 60 nm. Two magnetic Curie transition points (TC1 = 141 K, TC2 = 67 K) observed from the isofield magnetization measurement affirmed the short-range ferromagnetic behavior of Sm2NiMnO6 creating the continuous second-order transition followed by the discontinuous first-order transition. A minor cusp at 10 K confirmed the microscopic superparamagnetic behavior at low fields apart from the dual magnetic phase transition. Adiabatic demagnetization of Sm2NiMnO6 nanoparticles was measured in terms of magnetic entropy, and the magnetic refrigerant capacity was calculated to be 0.44 J kg−1 K−1 and ~ 20 J kg−1 respectively. © 2020, Springer Nature B.V.