To study the potential of phosphorus (P) release from sediments in the lakes: Chełmżyńskie and Wieczno Płd. was the aim of this study. The task was realized by carrying chemical sequential extractions. The novelty of our approach consists in adopting the SPLITT (split-flow lateral-transport thin) method of particles separation, which was used supplementary to sieving. Sieving provides following sediment fractions: 0.25–0.5, 0.125–0.25, 0.09–0.125 mm, whereas the SPLITT allows separation of particles which smaller than 30 μm, and which constituted >30 % of total sediment mass. The mass distribution of size fractions in sediments from both the lakes was very similar. P content, as the sum of HCl-P, NaOH-P, NH4Cl-P, was by ca. 20 % lower in the particle size fractions 0.25–0.5, 0.125–25 mm, whereas total P content in SPLIT sediment was much higher in all size fractions (