Resumo. Jatobá-Mirim species belongs to Fabaceae family and is distributed through Pantanal and Caatinga areas. Its wood is suitable for the construction and the manufacture of luxury furniture and is recommended for urban forestry and used to compose heterogeneous reforestation. Taking into account their potential use this work was developed with the objective of evaluating the effect of different temperatures on the germination rate and initial root growth of Jatobá-Mirim seeds. The seeds used in this experiment were harvested at ‘Cabeceira do Prata’ farm, located in ‘Jardim’ municipality, in Mato Grosso do Sul state, in September 2009. The material collected was transported to the Laboratory of Research on Bio-diversity and Environmental Systems at Anhanguera-Uniderp University where the research was developed. The seeds were submitted to constant temperatures of 20, 25, 30, 35 °C and alternated temperatures of 20- 30 and 25-35 °C, in six treatments, kept in germination cameras of B.O.D type. The obtained results show that the best temperatures for the seed germination are 30 o C (90%), 35 °C (97%) and 25-35 °C (90%), statistically equal, certifying that those temperatures are more efficient to promote the germination. Taking into account the mean time for germination, germination speed index and dry matter production, constant temperatures of 30 and 35 o C are better and its results, statistically equal and higher than other treatments.