Introduction. The purpose of this work is to study the thermally modified peat additive, the use of which is scientifically justified in the works of professor N.O. Kopanitsa and her colleagues. This additive is extracted from the raw materials from the Kaliningrad region, and the authors focus on its effect on the consistency, moisture-retaining capacity of the mix, and the strength characteristics of fine-grained concrete.Materials and methods. The additive was made from lowland peat extracted from the Glushkovo quarry in the Kaliningrad region. Raw materials were subjected to thermal treatment with limited access of oxygen.Results. The authors have proven an increase in the consistency and water-retaining capacity of mixes that have 4 and 8 % additive. On the 21 day, an 9 % increase in the flexural strength of concrete specimens with the 4 and 8 % additive was registered in comparison with the benchmark specimen (5.5 MPa for the benchmark mix and 6 MPa for the 4 and 8 % additive); an increase in compression strength reached 23 % when the 8 % additive was used (40.7 and 50.2 MPa for the benchmark mix and the one that contains the 8 % additive, respectively).Conclusions. The presented results of the research show a strong potential for the improvement of physical-mechanical properties of concretes by using thermally modified peat additives made from the local raw materials extracted in the Kali­ningrad region.