Treatment effect of benzyladenopurine (BA) used to block the lateral roots formed on soybean sprouts should be influenced by its applying methods. This study was done to check the effects of temperature and period from seed imbibition into 2 ppm BA solution to the first watering for sprout culture on growth and morphology of soybean sprouts. Imbibed three cultivar (cv. Pungsannam- ulkong, Sowonkong and Junjery) seeds for 5 hours into 2 ppm BA solution were placed under different temperatures (AT; 20, 30, 40℃) and periods (AP; 0, 1, 2, 3, 4 hours). On the 6th day, the soybean sprouts were classified by 4 categories on the base of hypocotyl length; > 7 cm, 4 to 7 cm), < 4 cm and non-germination to calculate their composition rates, number of lateral roots, lengths of hypocotyl and root, diameters at middle and hook of hypocotyl, and fraction dry weights were measured. Germination and growth responses of the cultivars were changed by AT and AP treatments. The responses, lateral root formation and fresh weights were, however, mainly affected by the cultivars used rather than AT treatment. Rate of the sprouts which formed lateral roots was decreased with increased periods to 4 hours, but their number per sprout was not different between the treatments of longer than 3 hours. Lengths of hypocotyl and root, organ and total fresh weights were the highest in an hour AP treatment although longer than 3 hour AP treatments did not showed the significant difference in the lengths. Conclusionally AP treatment was more important than AT one in seed aeration for soybean sprout culture immediately after imbibition into BA solution, and was done at least for 3 hours.