The article presents the results of a detailed study of the geological structure of the Łeba Barrier in the Rąbka cross-section (Southern Baltic, Poland). The barrier separates Lake Łebsko from the Baltic. Five sedimentary complexes were distinguished there (M2-M6). The spatial variability of the grain-size distribution was examined and succession stages of the mollusc fauna occurring in the individual sedimentary complexes were distinguished. Radiocarbon dating was used to establish the age of the most important events during the process of formation of the barrier, which took place in the course of several relative sea-level changes. The first sedimentary complex (M2) at Rąbka is connected with the second ingression (i2) of the Baltic Sea (ca. 6,700-6,000 14C years BP), sea-level stabilization (6,000-5,500 14C years BP), and at last sea-level lowering (5,500-5,000 14C years BP) in the region of the Gardno-Łeba Coastal Plain. The sedimentary complex M3 developed in a lagoonal environment when the barrier was situated north of its present position (5,000-3,000 14C BP). The next lowering of the sea-level made the lagoon shallower and caused the emergence of small but already subaerial stretches of barrier land with a freshwater fauna in the north (4,880š40 14C BP). With the next ingression stage (i3), which took place between 4,500 and 3,000 BP, the barrier shifted to its present-day position and the lagoon changed into a freshwater lake. From 3,000 to 1,700 14C BP fossil soil and peats developed on the barrier surface as a result of another sea-level lowering. The last ingression stages (i4 and i5), younger than 1,700 BP, built up the barrier, practically in its today's location (sedimentary complexes M4 and M5). The youngest sedimentary complex (M-6) is represented by present-day beach sands.