To understand the free surface roughening phenomena of polycrystalline metals, the surface roughening behaviors of three kinds of metal sheets were investigated under uniaxial tension. The materials used were AZ31 magnesium alloy, SPFC 590Y steel, and A5052-O aluminum alloy. In the in-situ observation of surface roughening for AZ31 magnesium alloy, it seemed that the surface of each grain roughened independently and the roughness increases with increasing plastic strain. In contrast to A5052-O and SPFC, the anisotropy of free surface roughening was observed for AZ31 magnesium alloy. Compared with planar anisotropy , the microscopic anisotropy of surface roughening is not related to . In AZ31 magnesium alloy, the anisotropy of surface roughening arises and, instead of the r-value, another parameter is needed to evaluate the anisotropy of free surface roughening.