Fully dense few-layer graphene (FG)/Al₂O₃ nanocomposites with homogeneously dispersed FG in matrix are prepared by using a heteroaggregation method followed by spark plasma sintering. It is found that the two dimensional FG has great ability to restrain grain growth in comparison to other inclusions. In addition, the morphology of grain in composite is modified by the addition of FG during densification process compared with monolithic alumina. Thanks to the greatly decreased grain size, the composites are almost as hard as monolithic alumina at low sintering temperature (1573 K) even if graphene content is as high as 1.2 vol.%. However, at higher sintering temperature (1673 K), the hardness of composites decreases further but the change in elastic modulus is very limited. The decline of hardness and elastic modulus mainly arises from the sliding feature of FG, low modulus of reduced graphene oxide in both in-plane and out-of-plane directions.