Cell derivatives have received increasing attention due to their unique ability to mimic many of the natural properties displayed by their source cells. Integration of cell-derived natural materials with synthetic subjects can be applied toward the development of novel biomedical nano/microscale devices for a wide range of applications, including drug delivery and biodetoxification. Herein, a cell membrane functionalized magnesium-based Janus micromotor, powered by water, that mimics natural motile cells is reported. The new cell-mimicking Janus micromotor is constructed by integrating red blood cell (RBC) membranes, gold nanoparticles (AuNPs), and alginate (ALG) onto the exposed surface areas of magnesium microparticles that are partially embedded in Parafilm. The resulting RBC membrane-coated magnesium (RBC-Mg) Janus micromotors display an efficient and guided propulsion in water without any external fuel, as well as in biological (albumin-rich) media with no apparent biofouling, mimicking the movement of natural motile cells. The effective RBC membrane coating bestows the RBC-Mg Janus micromotors with unique capability for absorbing and neutralizing both biological protein toxins and nerve agent simulants. Such detoxification ability is facilitated greatly by the water-driven motion of the motors. The RBC-Mg Janus micromotors represent an exciting progress toward cell-mimicking microscale motors that hold great promise for diverse biomedical and biodefense applications.