the imbiru？u [pseudobombax longiflorum (mart. et zucc.) a. robyns] is an arboreous species that occurs in the brazilian savannah. the exploitation and destruction of this biome have reduced the p. longiflorum populations and studies on its germination are crucial for preserving it. this study aimed to evaluate the germination process of two populations of p. longiflorum seeds, on different substrates. a completely randomized design, in a 2x5 factorial scheme (two populations x five substrates), was used, with five replications of 50 seeds for each treatment. the sampled populations were collected in rondonópolis and cuiabá, in the mato grosso state, brazil. substrates consisted of black soil, vermiculite, sand, black soil + vermiculite (1:1) v/v, and black soil + sand (1:1) v/v. the germination percentage of viable and dead seeds, seeds with fungi, and the mean germination time were evaluated. the highest germination rate was observed in the sand substrate (78%), in seeds from cuiabá, and in the sand and vermiculite substrates (36.6%), in seeds from rondonópolis. the mean germination time ranged from 10.6 to 16.5 days, for the seeds from rondonópolis, and from 14.7 to 18.1, for the ones from cuiabá. the seeds from rondonópolis, in the black soil substrate, presented a 66.7% mortality rate, with the presence of the fusarium and rhizoctonia fungi genera. the p. longiflorum seeds from cuiabá showed a higher germination rate than those from rondonópolis, being the most suitable ones for the seedlings production. the sand substrate is the recommended one for the p. longiflorum seeds germination due to its greater ease of acquisition and lower cost.