Collisions of helium clusters with size-selected cobalt cluster ions, Co-m(+) ( m < 5), were studied experimentally by using a merging beam technique. The product ions, Com+Hen (cluster complexes), were mass-analyzed, and this result indicates that more than 20 helium atoms can be attached onto Co-m(+) at the relative velocities of 10(3) m/s. The measured size distributions of the cluster complexes indicate that there are relatively stable complexes: Co2+Hen (n = 2, 4, 6, and 12), Co3(+)He(n) (n = 3, 6), Co4+He4, and Co(5)(+)H(e)n (n = 3, 6, 8, and 10). These stabilities are explained in terms of their geometric structures. The yields of the cluster complexes were also measured as a function of the relative velocity (1 x 10(2)-4 x 10(3) m/s), and this result demonstrates that the main interaction in the collision process changes with the increase of the collision energy from the electrostatic interaction, which includes the induced deformation of He-N, to the hard-sphere interaction.