The objetive of this work was to evaluate the effect of temperature and osmotic potential on imbibition and the radicle emergence of onion seeds. Two experiments were carried out. In the first one seeds were imbibed during 12 days in destilated water and osmotic solutions with polyethylene glicol, molecular weigth 6000 (PEG 6000) at -0,5, -1,0 and -1,5MPa. The rate and final emergence of radicle and the seed moisture content were evaluate. In the second one, the seeds were imbibed in destilated water and PEG 6000 solution (-0,75MPa). The imbibition was evaluate at 72 hours and eight days, respectively at 10, 15, 20 and 25°C. The imbibition and radicle emergence was slower in osmotic potencial between -0,5 and -1,-0MPa. At -1,5MPa the radicle emergence was suppressed at 12 days test period. The seeds induced the radicle emergence with 44,2 at 46,8% moisture content under water destilated and 44,1 at 46,1% in PEG 6000 solution (-0,75MPa). The seed imbibition rate under destiiated water increased in the range at 10°C and 25°C and was faster than PEG 6000 solution (-0,75MPa).