Recently friction stir processing (FSP) has emerged as an effective tool for enhancing sheet metal properties through microstructure modification. Significant grain refinement and homogenization can be achieved in a single FSP pass leading to improved formability, especially at elevated temperatures. FSP is a solid-state process where the material within the processed zone undergoes intense plastic deformation resulting in dynamically recrystallized grain structure. Most of the research conducted on FSP focuses on aluminum alloys. Despite the potential weight reduction that can be achieved using magnesium alloys, very little is reported on FSP of magnesium alloys. In this work, we examine the possibility of using FSP to modify the microstructure and properties of commercial AZ31B-H24 magnesium alloy sheets. The effect of various process parameters on thermal histories, resulting microstructure and properties are investigated. Preliminary results are promising and it is shown that FSP leads to finer and more homogenized grain structure.