Poor surface properties of magnesium alloys limit their extensive use in many applications. Laser surface engineering can be used to enhance surface-related properties of Mg alloys, and the purpose of this paper is to study the effect of laser pulse duration on surface of AZ91D Mg alloy. After millisecond-pulse laser treatment, ripples and cellular/dendrite as well as nanoscale -Mg17Al12 precipitates in the -Mg matrix were found in the surface microstructure, moreover, the melt depth was more than 150 micron. After nanosecond-pulse laser treatment, craters of 10 to 50 micron in diameter were observed on the surface due to plasma expansion and melted matter ejection during local boiling process, and the melt depth was nearly 15 micron. However, femtosecond-pulse laser treatment produced various micro- and nano-structures within a very thin layer on the surface.