In total, 550 species of longhorn beetles (Cerambycidae) exist in Europe. The most recent checklist of Cerambycidae family of Serbia cited 265 species and 92 subspecies, belonging to 109 genera, 48 tribes, and six subfamilies in the country. However, the presence of 28 species reported from Serbia is questionable. Here we present the first finding of Phytoecia (Musaria) argus (Frölich, 1793) for the fauna of Serbia. The species was collected in May and June 2018 on Stol mountain (near the town of Bor, eastern Serbia). Additionally, data on morphology, bionomy and distribution of the longhorn beetle species are given. With this finding, the total number of longhorn beetle species in Serbia is estimated at 266. This species could be used as an indicator for the assessment of the nature value and conservation status of natural habitats in Serbia and Europe.