Actinidia rufa is native to the south western region along the pacific coast of Japan and adapts well to warm climate. It has tolerance to hot weather in summer and strong winds of typhoons. The fruit is relatively small but edible. For the purpose of improving kiwifruit adaptable to low chilling regions by utilizing the traits of A. rufa, the chilling requirement was determined in the kiwifruit cultivars, A. rufa and their interspecific hybrids. Cuttings were collected at different chilling exposition and incubated at 23 degrees C with 16 h of illumination. At 0 CH (chilling hour), just before the natural accumulation of chilling started, the buds burst in all strains of A. rufa and bursting rate ranged from 25 to 60% after 4 weeks. At 300 CH, the rate reached above 80%. In A. chinensis, diploid cultivars burst at 0 CH, but the bursting rate varied largely from 0 to 90% after 4 weeks. At 300 CH, all cultivars of diploid A. chinensis burst and bursting rate reached 100% in most cultivars, but it remained below 20% in several cultivars. In contrast, in tetraploid cultivars of A. chinensis, bud burst occurred infrequently at 0 CH. At 300 CH, the bursting rate largely varied from 0 to 60%. In A. deliciosa 'Hayward', no bud burst was observed even at 300 CH. In the interspecific hybrids between A. rufa and diploid A. chinensis, the bud burst occurred in all selections even at 0 CH. However, the bursting rate ranged from 20 to 95% after 4 weeks. At 300 CH, the bursting rate of all strains reached as high as 90% within 2 weeks. These results suggest the possibility of selecting for low chill kiwifruit strains adapted to warm conditions from the interspecific hybrids.