This paper is an attempt to determine the effect of technological parameters of milling on the surface roughness of the AZ91D magnesium alloy. The cutting tool used in tests was a TiAlN-coated carbide milling cutter. The milling tests were carried out at variable cutting speed, feed per tooth and depth of cut, and the results were compared. The analysis was based on the 2D roughness parameters measured on the end and lateral faces of specimens, as well as on the 3D roughness parameters measured on the specimens’ end faces. The test results indicated that the increase in the feed per tooth results in the increase in the value of 2D and 3D surface roughness parameters. It was found that cutting speed and axial depth of cut have negligible effect on the 2D roughness of the workpiece surface, whereas the increase in cutting speed results in the reduction of the 3D surface roughness parameters.