The influence of Co on the microstructure, phase transformation temperature, mechanical properties and shape memory effect of TiNiNb alloys has been investigated by X-ray diffraction, differential scanning calorimetry, tensile stress–strain measurements and bending tests, respectively. The results show that the addition of Co suppresses the brittle (Ti,Nb) 2Ni phase of NiTiNb alloys, and the phase transformation temperature and lattice parameter of Ni 46.5− x Ti 44.5Nb 9Co x alloys are decreased with the increase of Co content. The yield strength of NiTiNb alloys has been improved due to the addition of Co. In particular, Ni 45.5Ti 44.5Nb 9Co 1 alloy exhibits highest yield strength among the Ni 46.5− x Ti 44.5Nb 9Co x (Co = 0.5, 1, 1.5, 2) alloys, and a maximum completely recoverable strain of 7.8% has been achieved.