The Kastro peninsula constitutes the extension towards the West of Myrina, the Lemnos capital, on the western coast of the island, in the North Aegean Sea. The ongoing research project on rock-cut features and rock-art of this complex site included a five-year (2002–2007) subsurface investigation, during which, among other mobile finds, charcoal and seashell samples were also collected, associated in situ to rock-cut features. Subsequently, in an attempt to bring about information on the dating of the rock-cut site, an investigation based on 14C has also been undertaken. Therefore, the purpose of the present paper is the AMS dating of the unearthed anthropogenic deposits and the calculation of the regional marine reservoir effect during the end of the Late Bronze Age. Our results show that the age of the deposits is spanning from the 13th century BC till the 6th century AD. Moreover, the 14C ages of two pairs of charcoal-seashell samples showed that the mean marine reservoir age R(t) in this region from the 13th to the 10th centuries BC is 175 ± 59 14C yrs and the mean local sea surface reservoir deviation ΔR is found to be –288 ± 108 14C yrs (within 1σ).