This paper reports an in-situ study of the plastic deformation behavior of surface grains in a polycrystalline aluminum alloy, in particular the active slip systems and lattice rotation, by means of the electron backscattered diffraction method. The experimental analysis is conducted at a spatial resolution of 1. μm, thus allowing detailed analysis at subgrain levels, enabling elucidation of fine details of the deformation process that are not commonly seen in the literature. It is found that the grains rotate gradually with increasing strain during tensile deformation. The lattice rotation, in terms of both rotation path and rotation rate, is highly inhomogeneous both among the grains and within individual grains, leading to the formation of subgrains. The rotation behavior can be adequately described by the activation of slip systems with the maximum and second maximum Schmid factors. The number of independent slip systems in surface grains is much fewer than that in interior grains, as predicted by crystal plasticity theories. The lattice rotation rate is also heterogeneous among grains and subregions and for different deformation stages. The differences in rotation rate provide another mechanism for the accommodation of plastic strains and for the creation of subgrains. These findings are of importance for the mechanical processing of thin sheet materials or the deformation behavior of miniature components, where the majority of grains are on the surfaces. © 2013 Elsevier B.V.