In situ synthesis of multiwalled carbon nanotubes (MWCNTs) was performed by chemical vapor deposition of methane on a LaNiO3 perovskite-type growth-promoter prepared by the sol–gel method. The as-produced MWCNTs were purified via a two-step procedure consisting of an oxidation in air and subsequent HNO3 treatment. Nearly monodisperse cobalt nanoparticles with an average size of 11.3 nm have been successfully decorated on MWCNTs by an impregnation–reduction method. The properties of the as-produced carbon nanotubes (CNTs) and Co/CNT catalysts were analyzed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). It was found that the reduction of LaNiO3 and formation of CNTs occur almost simultaneously under methane atmosphere and that the in situ controlled synthesis of MWCNTs with relatively high purity and uniform diameters could be realized by the chemical vapor deposition method in a tubular reactor. The catalytic activity of the Co/CNT catalyst was tested for the hydrolysis reaction of sodium borohydride (NaBH4) in basic medium to produce hydrogen. The prepared Co/CNT catalyst calcined at 300 °C shows high catalytic activity for hydrogen generation from hydrolysis of NaBH4.