<p>Ultra-small mill-grinding (USMG) tool is a compound tool that has both micro milling blades and grinding abrasive grains, which has both milling and grinding abilities. In this study, the mill-grinding properties of titanium in USMG on no more than 200-µm scale were investigated. A force model of side mill-grinding was proposed, which considers the effect of micro scale, abrasive grain size, and the joint action of milling blades and abrasive grains. Validation experiments were conducted using self-prepared electroplating mill-grinding tools with diameters 200&#xa0;µm. The influences of side mill-grinding parameters on the processing surface and forces were studied. The mill-grinding force on normal direction is the largest in three directions, which increases with the increasing of feeding velocity and decreases with the increasing of rotation speed. As the feeding velocity increases and rotation speed decreases, surface defects increase. Three types of surfaces were found, which are the surface with some small material agglomerations, uneven surface with many big material agglomerations, and the surface with fish scale like textures. Application experiments were conducted on the milled slots of titanium tubes, and a defect cleaning process method using slot mill-grinding technology was proposed. The micro mill-grinding tools were inserted into the milled micro slots of titanium tubes to remove the defects formed during micro milling. The influences of slot mill-grinding parameters on surfaces and structures of micro slots were investigated. As the feeding velocity increases and rotation speed decreases, the defects on surfaces and structures of micro slots increase.</p>