The recent developments in science and technology lead to the miniaturization of components in fields like aerospace, biomedical, and electronics. Due to the small tool dimensions and premature tool failure, the tool wear behavior is complicated in micro endmilling of difficult-to-cut materials. In this work, the influence of size effect on wear behavior of AlTiN-coated WC micro endmill and its effects on surface roughness, burr formation, and chip formation during machining on Inconel 718 was studied. It was found that adhesion, delamination, chipping, cutting edge rounding, and flank wear are the significant wear behaviors on AlTiN-coated WC micro endmill during machining of Inconel 718. Workpiece adhesion was observed to be severe in the plowing dominant region. The tool life with 6-mu m feed/tooth was found to be 60% more than that with 0.5-mu m feed/tooth. The tool failure criteria based on the width of flank wear and cutter edge radius were observed close to 27 and 9 mu m, respectively. The feed/tooth adjacent to cutting edge radius was observed as the most favorable cutting condition for good tool life and surface quality.