The effects of substituting Cu for Mn on the magnetocaloric, transport, and thermomagnetic properties of Ni50Mn35-xCuxIn14B (x = 0, 1.25, 2.0) Heusler alloys were studied. It has been found that the magnitude of the magnetization jump at the martensitic transformation decreased with increasing Cu concentration. Smaller magnetic entropy changes (∆SM) were observed for the alloys with higher Cu concentrations. A decrease in the resistivity was observed with increasing Cu concentration. The magnetoresistance was dramatically suppressed with increasing Cu concentration due to the weakening of the antiferromagnetic (AFM) interactions in the martensitic phase. The experimental results demonstrate that Cu in Ni50Mn35-xCuxIn14B Heusler alloys suppresses the AFM interactions and enhances the ferromagnetic (FM) interactions in these alloys. Possible mechanisms responsible for the observed behavior are discussed.