IrO2 nanocrystals (NCs) were grown on vertically aligned carbon nanotubes (CNTs) forming IrO2/CNTs nanocomposites by metal organic chemical vapor deposition using (C6H7)(C8H12)Ir as a source reagent. The surface morphology, structural and spectroscopic properties of the nanocomposites were characterized. Micrographs of field-emission scanning electron microscope showed that the surface morphology of the as-deposited IrO2 NCs varied from particle-like to tube-like NCs as the deposition time increased from 5 to 60 min. The transmission electron microscope image of IrO2/CNTs nanocomposites revealed that IrO2 NCs had been deposited onto the surface of the CNTs with uniform size distribution and random directions. X-ray diffraction pattern confirmed the formation of pure rutile IrO2 NCs on CNTs. The redshifts of the peak positions and broadening of linewidths of the IrO2 Raman features were attributed mainly to the size effect. The particles-like IrO2 NCs may be used as a protective layer on CNTs, providing stable and uniform field emission application. While the nanotube-like structure may increase the surface-to-volume ratio which makes the IrO2/CNTs nanocomposites as an attractive candidate for the supercapacitor application.