The effects of the partial substitution of Mn by Co on the magnetic, magnetoelastic, and magnetocaloric properties of Ni50Mn35In15 Heusler alloys were studied using x-ray diffraction, temperature and field dependences of the magnetization [M(T,H)], and strain gauge techniques. It was observed that the presence of ~3% Co atoms in Mn sites strongly affected the magnetic and magnetoelastic behaviors of Ni50Mn35In15. At H=5 T, a maximum magnetoelastic strain of ~0.6% was observed for Ni50Mn35In15. It was found that Co substituted into the Mn position does not affect the Delta SM in the vicinity of the second order transitions (SOTs), however Delta SM near the first order transitions (FOTs) it slightly decreases. The net refrigeration capacities in the vicinity of both the FOT and SOT were found to significantly increase by introducing Co into Mn sites. The net refrigeration capacity in the vicinity of the FOT and SOT was found to be 167 J/kg (T =277–293 K) and 229 J/kg (T=305–354 K), respectively, at a magnetizing field of 5 T. These values of the magnetocaloric parameters are comparable to that of the largest values reported for metallic magnets near room temperature. © 2010 American Institute of Physics.