Among the speed tests that allows to determine the viability and vigor of seeds, the tetrazolium test is one of the most promising alternative. However, it is necessary to establish a specific methodology for each species studied. Thus, this present work was realized with the aim to adequate the methodology of tetrazolium test to evaluate the viability of canafistula(Cassia grandis L. F.). Were evaluated the following procedures to the removal of seeds coat: moistening in paper towel and immersion in water by 24 hours 30°C in an incubator type BOD. Then, the embryos were immersed in 0,075%, 0,5% and 1% of tetrazolium solution at 30°C in the dark for 4, 8 and 12 hours for the color development. Between the tested procedures to the removal of seeds coat, the immersion of seeds in water at 30°C for 24 hours allows better imbibition of seeds. Uniform coloration was obtained when seeds were immersed in tetrazolium solution at 0,5% for 8 hours at 30°C in the dark. The vigorous tissue was colored by brilliant pink, while the tissues with some deterioration or with damages presented the coloration of red-carmine intense. It was possible to establish three viable classes of seeds (class 1, 2 and 3) and three non-viable and dead (class 4, 5 and 6).