Using the first principles method, we study the growth behavior and electronic and magnetic properties of TiNin (n = 1-12) clusters to clarify the effect of Ti modulation on the nickel nanostructures. Furthermore, chemisorption of H2 was studied to understand the chemical reactivity of H2 on the small Ni- and Ti-doped Ni clusters. The calculations are performed using the plane wave pseudopotential approach under the density functional theory and generalized gradient approximation for the exchange and correlation functional. The optimized geometries of TiNin-1 clusters indicate that the substitution of Ti brings a substantial structural reconstruction from 3D structure to a layer structure in which Ti atom is found to coordinate with Ni atoms to a maximum extent. This is accompanied by a significant enhancement in binding energies and reduction in chemical reactivity. Furthermore, the magnetic moments of the small Ti-doped Ni clusters are quenched because of the antiferromagnetic alignment of the Ti electrons. The lowest-energy structure of H2 chemisorbed on Ni clusters shows that hydrogen prefers to adsorb on the edge site with two hydrogen atoms on these clusters in neighboring sites as the preferred arrangement. The incorporation of Ti atom improves the chemisorption energy of Ni clusters. Bader charge analysis indicates that with the formation of metal hydride, the H atoms withdraw charges from the metal centers, making them lose an electron, and carry a positive charge over them. Furthermore, Ti doping is found to enhance the chemical reactivity of Ni clusters.