The need to investigate species used in forest exploitation and the disposal of their residues and byproducts motivated the evaluation in a greenhouse of the effect of wood vinegar (WV) on seed germination and seedling growth of leucaena (Leucaena leucocephala (Lam.) de Wit) in two substrates. The studied factors were WV concentrations in irrigation water (0.0, 0.4, 0.8, 1.2 and 1.6%) and substrate (sand or vermiculite). Each treatment had four repetitions of 30 seeds in plastic trays. The variables evaluated up to 27 days after sowing were: emergence percentage, emergence speed index, percentage of ungerminated seeds, total seedling length, shoot height, shoot and root dry weight. The concentrations of wood vinegar used in this study had an inhibitory effect on the germination, emergence and initial development of leucaena at all studied concentrations. A large decrease in percentage and speed of germination of leucaena was observed, mainly in the sand substrate. The more intense effect on the germination stage than in later stages of development was caused by substances contained in WV, such as acetic acid, furfural and methanol. The germination, emergence and initial growth of leucaena were less impaired when the substrate was vermiculite. For effective control of leucaena it is necessary to test higher concentrations of wood vinegar.