The ultramicrohardness distribution near the interface in the matrix of some aluminum matrix composites is investigated. The results show that, in metal matrix composites (MMCs), with increase in distance to the reinforcement-matrix interface the ultramicrohardness presents a progressively decreased gradient distribution in the matrix. The non-uniform distribution degree (NDD) can be defined by the ratio between the maximum hardness near the interface and the average hardness far away from the interface. The relative dimension of the gradient distribution area (RDGDA) can be defined by the ratio between the absolute dimension of the gradient distribution area (ADGDA) and the reinforcement size. The NDD varies to a great extent, of the order of 1.45-10.0, which is strongly related to the composite system (reinforcement size, morphology, interspaces, matrix composition), fabrication condition and heat treatment. The RDGDA is about 0.2-2.0. A larger reinforcement size and angular shape of reinforcement would lead to a higher NDD and smaller RDGDA. In addition, adding proper elements into the matrix, lowering fabrication temperature, increasing cooling rate and carrying out thermal cycling would result in a lower NDD. But the aging treatment would produce a larger NDD.