In recent years, cobalt attracted large interest in biological application, due to its biocompatibility and low toxicity. The synthesis of Co doped ZnO/MWCNTs hybrid by a wet chemical process been reported. The results confirmed prevailing that it is the size of Zinc Oxide NPs by determines the concentration of precursor. The effect of changing the concentration of Co doping on the physical properties of the prepared samples was investigated. The X ray diffraction showed the formation of hexagonal wurtzite structure of zinc oxide with disappearance the diffraction peaks from cobalt. The crystalline size average increased from 25.66 to 33.33 nm with increasing concentration of cobalt. FESEM images confirmed the success of the growth of spherical clusters over the surface of interlocking cylindrical tubes and their association with a crimped surface. This indicates a formation Co doped ZnO\MWCNT hybrid. In contrast, the UV–Vis spectra revealed that all hybrid nanostructures have high absorbance as well as the band gap narrowing with increasing cobalt doping concentration, the band gap values of Co doped ZnO/MWCNTs hybrid with Co (2%, 4%, 6%, 8%) are 3.29, 3.04, 2.99, and 2.97 eV, respectively. Moreover, the antibacterial effect reveals that, the synthesized Co doped ZnO/MWCNTs hybrid has high activity toward the Gram positive and Gram negative bacteria High inhibition efficiency shown about (17.8–22) mm for E. coli and (19.5–20.5) mm for S. aureus at high concentration of Co dopant.