In this study we describe a new species of the click-beetle genus Lacon Laporte, 1838 from the relict Hyrcanian forest in northern Iran. Lacon mertliki sp. nov. is morphologically similar to L. lepidopterus (Panzer, 1801) but differs from the latter in the body coloration and pubescence, the shape of pronotum and scutellar shield, and male and female genitalia. We provide brief data on its ecology as well as an identification key to all Lacon species in Iran. Additionally, we synonymize Lacon nadaii Platia & Németh, 2011 with Lacon unicolor (Candèze, 1874).