<p>Cutting force measurement serves as an effective approach to monitor machining states during milling process. In this paper, a novel tool holder integrated with piezoelectric force sensors was proposed for three-axial milling force measurement. A force measurement module was designed utilizing five symmetrically arranged piezoelectric force sensors, with considering both high-sensitivity detections of three-axial forces and high rigidity of the tool holder. Finite element modeling and design of structural parameters were carried out for the force measurement module to realize both high rigidity and high force transmission efficiency simultaneously. Static tests showed a force measurement sensitivity of over 18.6 mV/N and a low linearity error of less than 0.63% for all three axial directions of the proposed tool holder. Milling experiments were conducted to verify the in-process force measurement capability of the proposed tool holder, which exhibits a high consistency compared with the results measured by a commercial standard dynamometer. The experimental results showed that the measured forces could accurately identify the cutting states of each cutting tooth of the tool during the milling process, and tool wear caused significant increase of amplitude of radial force, with a ratio of the tool wear length to the amplitude increase of the force of approximately 31.4&#xa0;μm/N.</p>