Structural, magnetic, magnetocaloric and mechanical properties of Ni49-xMn39Sb12Cox (x = 0,2,4) alloys prepared by arc-melting have been studied. It has been observed that with increase in Co content, the system transforms from martensite to austenite phase. Magnetic measurements show that the martensite transition shifts from 338 K to 290 K. The effective refrigerant capacity is found to increase from 23 J/kg to 119 J/kg with Co doping under an applied magnetic field of 7T. The adiabatic temperature change evaluated from zero field heat capacity was found to be −3.75 K in Co doped alloy at 7 T. Our studies show that Co doping in Ni-Mn-Sb alloy also improves mechanical properties of the alloy and thus can be considered as a competent magnetic refrigerant alloy. © 2020 Elsevier B.V.