Ecoregion Caatinga presents a great diversity of species with potential for exploitation. Among them ‘pereirovermelho’ (Simira gardnerianaM.R. Barbosa & Peixoto) stands out for its importance in timber and forestry activities. Its seeds germinate slowly. Therefore, the use of tetrazolium test to estimate viability becomes essential when quick answers on seeds quality are wanted. This study has aimed to establish the best concentration of tetrazolium solution and the coloration period for assessing the viability of Simira gardnerianaseeds. Initially, seeds were subjected to pre-wetting between paper sheets for 144 hours at 30 °C. Subsequently, the endosperm portion containing the embryo was immersed at four concentrations of
tetrazolium solution (0.075, 0.1, 0.5 and 1.0%) and three coloration periods (2, 4 and 6 hours) in the dark under the temperature of 30 °C and another one at 35 °C. The percentage of viable seeds was compared with the results obtained in the germination test conducted on paper substrate at 30 °C in four replicates of 25 seeds. Tetrazolium test was efficient to estimate the viability of S. gardnerianaseed and the concentration of 0.075% for six hours at 35 °C was the best condition.