Resumo. The properly composted sewage sludge (biosolid) presents significant amounts of organic matter and nutrients to the plant growth in its composition. Therefore, its utilization in a substrate composition for the seedlings production comes to represent, more than an environment benefit, a great choice from the technical and economical angle. This project aims to characterize biosolid substrates and commercial substrate chemically and physically, and to estimate their potential to generate Schinus terebinthifolius Raddi. and Handroanthus heptaphyllus (Vell.) Mattos seedlings. Different volumetric proportions of biosolid (BIO) mixed with commercial substrate (SC) were tested for tube seedlings production, consisting in the following formulas: T1 = 0% BIO + 100% SC; T2 = 25% BIO + 75% SC; T3 = 50% BIO + 50% SC; T4 = 100% BIO + 0% SC. A hundred and thirty-four days after sowing, the following morphological parameters were evaluated, height (H), diameter (D), aerial part dry matter, (MSPA), root dry matter (MSR), height diameter ratio (HD), the ratio of aerial part dry matter and root dry matter (MSPAMSR), and the Dickson Quality Index (IQD). The bigger the substrates biosolid proportion was, the bigger the nutrient level was, mainly of N, P, K, and a bigger capacity of water retention was also found. The biosolid presented high potential for substrate composition in seedling production in the related species. The best results for Schinus terebinthifolius growth were observed in T3 and T4 treatments; for the Handroanthus heptaphyllus , the best results were observed in the T3 treatment.