Composites incorporating various vol.% (0.0, 1.1, 6.4, and 10.4) of multiwall carbon nanotubes (MWCNTs) in alumina were consolidated by the spark plasma sintering. Their thermal transport properties were investigated over the temperature range 300-800 K as a function of nanotube contents. It was observed that the temperature-dependent effective thermal conductivity decreases with the addition of MWCNTs in alumina. This behavior was analyzed in terms of phonon mean free path, elastic modulus, average sound speed, and interface thermal resistance. Compared with 1/T behavior for pristine alumina, a subtle decrease in temperature dependence of the thermal conductivity of the composites with the addition of MWCNTs is observed, indicating the presence of extra phonon scattering mechanism beyond the intrinsic phonon-phonon scattering. Simulation of experimental results with theoretical model shows that the large interfacial thermal barrier between MWCNTs and alumina plays a dominant role in controlling thermal transport properties of the composites. In addition to dominant interface thermal resistance other secondary factors such as nanotube agglomeration, processing defects, porosity also contribute for low thermal conductivity at the higher volume fraction of MWCNTs in the composite.