Bulk MgB2 sample with carbon nanotube (CNT)-coated Al addition was prepared by conventional solid-state reaction at 900°C for 30 min. We investigated the effects of Al and C co-doping on the lattice parameter, the microstructure, and the critical current density of MgB2. The substitution of Al and C atoms for the sites of Mg and B in the MgB2 lattice resulted in dislocations in the MgB2 grains, which makes great contributions, along with the nanoscale oxide particles, to the enhancement of critical current density at high field (103 A cm -2, 7 T, 5 K) in the co-doped sample. These results contrasted significantly with the measured values of the pure MgB2 and Al- and C-doped samples. Co-doping introduced more electrons into MgB2 and decreased both the parameters c and a of MgB2 lattice, and the used coating technique delayed and shortened the oxidation process of Mg and Al, leading to the decrease in the size and the content of the oxide. These advantages should be responsible for the enhancement of the critical current density as well. © 2014 Springer Science+Business Media New York.