Resumo. Abstract: Aim The increment of decomposition of organic matter in sediment samples from Nile tilapia farms was evaluated with the introduction of Bacillus subtilis and B. licheniformis bacteria. Methods Sediment samples placed in 18L plastic boxes received single dose inoculum with the following concentrations: 1.21 x 106 CFU g-1 (equivalent to 75 g ha-1), 2.41 x 106 CFU g-1 (equivalent to 150 g ha-1), 4.82 x 106 CFU g-1 (equivalent to 300 g ha-1) and 1.61 x 107 CFU g-1 (equivalent to 1000 g ha-1), in addition to a control treatment with saline solution only. Organic matter content, total organic carbon (TOC) and oxidizable (OOC), total nitrogen (TN), ratios (TOC: N and OOC: N), clay content, pH in water, Shoemaker, McLean, Pratt index (SMP Index), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) contents, potential acidity (H + Al), cation exchange capacity (CEC) at pH 7.0, base saturation (V) and sum of bases (S). Results The values of OM showed significant difference, between the lowest values (treatments 75, 150 and 300 g ha-1) and the highest value, (control treatment). TOC, OOC, NT and their relationships (TOC: N and OOC: N) showed significant differences between the mean values of the control treatment and the other treatments. Conclusions The addition of Bacillus subtilis and B. licheniformis bacteria increased the decomposition rate of organic matter in sediments samples from Nile tilapia farms.