Otočić Mrkan is the most SE of Cavtatski Otoci, a group of islets and above-water rocks in the approaches to Župski Zaljev. Otočić Mrkan is steep-to except for some above and below-water rocks close offshore and a chain of such rocks extending about 370 meters SE. The SW side of the islet is steep and rocky, the NW side overgrown with dark green bushes.