Heteroaggregation is employed in a controlled way to the mass-production of individually alumina-decorated multi-walled carbon nanotubes (CNTs) with optimized and controlled compositions, with the aim of obtaining reinforced homogeneously dispersed CNT–alumina matrix nanocomposite after spark plasma sintering. The homogeneous composites can only be obtained for CNT concentrations in the range 2.4–16vol.%. Irreversibility of decoration is examined, and homogeneity of the composite is further investigated, based on supernatant transparency proposed in our approach.