Sedimentological conditions and chemical characteristic of surface sediments were determined in twelve stations of the Píritu Lagoons in relation to the content and distribution of organic matter (C-org, N-org, total phosphorus, ratio C/N and reducing parameters (oxygen, permanganate and sulphur consumption) according to classical methodos of Geochemistry for marine sediments. Granulary sediments are constitutied by semi-fine sand (8.95%), thick slime (6.97%) and clay (76.50%) with predominance of clay + colloids (58.31%). According to the accumulative distribution curvem, the sediment deposition is very forced and is badly classified. Through the difraction analysis X rays of the argillaceous fraction, the presence of chlorita, goethita, muscovita, feldepar and quartz was detected, delimiting in this way the marine and earthen origin of minerals. The hydric contents of sediments (33.10-64.67%) was increased from the Mouth to the centre and west. C-org (0.71-3.17%) and N-org (0.07-0.34%) showed phenomena contrary to humidity and total phosphorus (0.09-0.32 %). C/N ratio (8.5-14.1%) indicate a balance between fresh material deposition and organic decumposition. High concentration of oxygen comsumption (92.78-319.94 ppm), permanganate (11 43-111.91 mg O2/g) and sulphur (0.30-12.60‰) dtermine a high reducing capacity of sediments from the Píritu Lagoons. The organic matter contents and reducing parameters show an independent behaviour except with C-org and N-organic, with a common source; thus indicating that the divergent chemical characteristics of sediments from the Píritu Lagoon are influenced by biotic and abiotic mechanisms and processes.