This is the first repot on the deformation behavior of Co-Cr-Mo biomedical alloy single crystals predominantly having an fcc structure. In the single crystal, one of four ε-variants was selectively formed, and its geometry was found to drastically affect the mechanical properties. The yield stress in the [111] orientation, in which the formation of ε-phase strain-induced martensite (SIM) crosses the grown-in ε-variant, was more than six times larger than that in the [1̅49] orientation, where SIM was formed parallel to the grown-in ε-variant. The intersection mechanism of the ε-variants is discussed via observations of the deformation microstructure.