Vibration problem during metal cutting occurs frequently in the manufacturing industry. The vibration level depends on many different parameters such as material type, dimensions of the workpiece, rigidity of tooling structure, cutting data and operation mode. In milling the cutting process subject the tool to vibrations and having a milling tool holder with long overhang, will most likely results in high vibration levels. These vibrations have a consequence of reduced tool life, poor surface finishing and disturbing sound. An investigation of dynamic properties of a milling tool holder with moderate overhang has been carried out by means of experimental modal analysis and vibration analysis during operating mode. Both angular vibrations of the rotating tool and vibrations of the machine tool structure were examined during milling. Also, bending motion of the rotating milling tool holder was examined during cutting. This paper focuses on identifying the source/sources of the dominating milling vibration components and to identify that of these vibrations which may be related to the structural dynamic properties of the milling tool holder.