We synthesize a carbon nanotubes (CNTs)/Co3O4 nanocomposite and demonstrate its electrochemical properties as an effective catalyst in Li-air cells. In particular, we introduce polydopamine as a binding agent (or reaction assistant) for CNTs and a catalyst with redox properties (Co3O4). Polydopamine coated on the surface of CNTs is expected to offer hydrophilicity and reactivity with oxide-sources. The CNTs/Co3O4 composite prepared using polydopamine layers shows homogeneously dispersed Co3O4 nanoparticles on the surface of the CNTs, thereby confirming that our new facile approach allows effective interaction between the carbon support and the oxide component. The air electrode containing polydopamine-assisted CNTs/Co3O4 composites shows superior catalytic activities in Li-air cells. This can be attributed to the wide catalytic-active area that provides well-dispersed nanosized Co3O4 particles as well as to the reduced contact resistance as a result of the close contact between CNTs and oxide (Co3O4).