Magnesium alloys are gaining popularity especially in the aerospace and automotive industries due to their very low density, enabling the manufacturing of lightweight components. In addition, good machinability contributes to the shaping of components of any shape. However, a significant difficulty in machining of magnesium alloys is their flammability, which forces the elimination of abrasive machining. Precision machining should therefore be considered to improve the quality of manufactured components. This study focuses on the observation and analysis of chip formation during precision milling of AZ91D magnesium alloy. The use of a high-speed camera allowed the exact observation at high magnification of the cutting zone and the phenomena occurring there. During the research, mainly an uneven performance of the cutting flutes of the end mill was observed. This resulted in the formation of chips with a significant difference in size.