Development of physiological maturation was studied on cedro (Cedrela fissilis Vell.) seeds in order to determine the best harvesting time. The reserch conducted at the Palma Farm and Seed Laboratory of the Federal University of Pelotas, included eight periods of fruit collect at 25 weeks after anthesis. The evaluation of the quality was made by determination of seed water content, dry weight, germination and electric conductivity of the seeds, and emergence velocity test and dry weight of seedlings. Also fruit color and dehiscence both were taken in consideration. Results showed that the physiologic maturity in cedro seeds occurs before dehiscence, within 29 and 31 weeks after anthesis, with seed water content ranging from 50 to 60% and, at the time, the fruits present a brown-greenish color or brown-clear. The best harvesting time of cedro seeds were obtained at 32 weeks after anthesis, with fruits present a brown color and initial dehiscence.