ENThis paper presents underwater relict forest fossil and ancient coast formation exploration results in the eastern Baltic Sea. Tree fossils and sediment layers discovered in the sea-bed were dated with 14C along with palynological and dendrological analysis. Based on the obtained data, a fragment of submerged early Holocene landscape, coastline of the Yoldia Sea and Ancylus Lake has been reconstructed. The research data determine that vegetation and natural conditions of the Yoldia Sea coastal were favourable for Early Mesolithic communities. Well-preserved relict pine forest dates are also crucial to Baltic Sea water level dynamics analysis during the period: end of Yoldia Sea-Ancylus Lake. Key words: Underwater relict forests, underwater archaeology, Yoldia Sea and Ancylus Lake coasts, Baltic Sea level fluctuations.