The effects of ball milling with simultaneous addition of multiwall carbon nanotubes (MWCNTs) on the thermoelectric properties of BiSbTe based nanocomposites were investigated in the temperature range from 300 K to 500 K. The MWCNTs in 0.5 vol% and 1.0 vol% were incorporated in fine BiSbTe powder that was processed from commercially available BiSbTe lumps and consolidated through pressure assisted induction heated sintering. The results show that the electrical and thermal transport properties of the composites are altered substantially. The thermal conductivity of the composites decreases significantly from pure BiSbTe bulk due to enhanced phonon scattering caused by nanostructuring and nanoinclusion effects. While the electrical conductivity deteriorates with the addition of MWCNTs, which is attributed partly to enhanced electron scattering and predominantly, rather low densification of the composites. The figure of merit of 1.0 vol% MWCNTs/BiSbTe composite remains close to that of pristine BiSbTe, snice the decrease in electrical conductivity is compensated by the significant reduction in thermal conductivity. The result suggests that optimizing the processing parameters for enhanced densification could improve the figure of merit for BiSbTe based MWCNTs composites.