In this work is presented a method that allows proper control of the nanoscale curvature of the external surface in multiwall carbon nanotubes (MWCNT), and shown its effect on the properties of Ni/MWCNT catalyst. After removal of residual nickel by treatment with HNO3 the external surface of parent CNT's was decorated with 15-17 nm nanoparticles of CaCO 3 (25 wt.%) by carbonization of deposited Ca-nitrate. The followed partial catalytic air-combustion of CNT's at conversions 30-50% modified the morphology of their walls. After removal of CaCO3 catalyst by treatment of the CNT's surface with HNO3 the modified nanotubes were decorated with metallic nickel by sonochemical deposition. The partial combustion of carbon constituting the CNT walls catalyzed by CaCO3 nanoparticles converts their structure from parallel grapheme layers to aggregates formed by grapheme onions with diameter of 5-12 nm. The nickel nanoparticles were located exclusively at the onions tops due to increasing the energetic barrier for metal adatoms (clusters) surface diffusion. It decreased the Ni crystal size from 8 to 2 nm at similar loadings of 50-60 wt.% and increased the catalytic activity in hydrogenation of chloroacetophenone more than twice.