The surface nano-deformation behavior in metal matrix composite during tensile loading was investigated by in-situ atomic force microscope (AFM) observation. The composite material used was aluminum matrix reinforced with 10 and 20 percent volume fraction of SiC particles. The average size of the reinforcement was 3 μm. Tensile test and in-situ observations were conducted using a loading device equipped with an AFM. Surface morphologies of the composite specimens were acquired before the loading and at various stages of the loading. The microstructural damage and the evolution of surface roughness were studied. The effect of volume fraction of the reinforcement on the nano-deformation behavior and damage evolution process of the composite based on nanoscale in-situ AFM observation will be discussed.