Young eucalyptus seedlings in general are sensitive to stress factors during early development and establishment. Weed competition is one of the major biotic effects contributing to reductions on the initial growth of eucalyptus plants. This study aimed to evaluate the effects of different densities and distances of Urochloa decumbens seeded and regrowth during the early growth of Eucalyptus urograndis. Two experiments were conducted in an open and semi-controlled area, in a completely randomized design, in factorial arrangement 4 × 2 + 1, being respectively, four densities of weed plants (2.6, 5.2, 7.8 and 10.4 plants m-2), two distances between Eucalyptus and weeds (5 and 15 cm), and a weed-free control. The height and diameter of eucalyptus were evaluated 15 days intervals, and at the end of 90 days after eucalyptus planting (DAP) the leaf area and dry mass were measured. For a density of U. decumbens plants that were seeded at a density of 2.6 plants m-2, 90 days after Eucalyptus planting (DAP), there was a decrease in the height (20%), stem diameter (10%), leaf area (55%) and dry mass (48%). For the regrowth of U. decumbens at a density of 2.6 plants m-2 at 90 DAP, the height (47%), stem diameter (55%), leaf area (89%) and dry mass (87%) decreased. The results demonstrate that U. decumbens adversely affected the growth of eucalyptus, without statistical differences between distances, and weeds in regrowth affecting Eucalyptus growth more than seeded weeds.