Lacustrine deposits from Ortel Królewski II (Eastern Poland) represent the Holsteinian Interglacial (MIS 11c). They are characterized by an extremely rich occurrence of ostracod and mollusc fauna. Collected samples represent pre-optimal part of the Holsteinian Interglacial corresponding to Picea–Alnus, Taxus and Pinus–Larix zones. Based on ostracod assemblage analysis a depth of the paleolake, the energy of the environment and the average January and July air temperature were reconstructed. Ostracods from Ortel Królewski II indicate a lake with possible periodic overflow sur- rounded by periodically flooded grasslands, which existed in the study area during the pre-optimal part of Holsteinian Interglacial.