Jacaranda mimosifolia, which has beautiful, long-lasting blue flowers, is a subtropical tree native to northern Argentina. It has been widely planted, not only in subtropical, but also in temperate areas where there is no risk of frost. We are conducting a breeding program for jacaranda aiming to select for dwarf and juvenile flowering characteristics that are suitable for potted plants. J. cuspidifolia, which has reddish-purple flowers and larger leaves than J. mimosifolia and is also distributed in northern Argentina, has juvenile flowering characteristics. We attempted interspecific crossing between J. mimosifolia and J. cuspidifolia. A relatively high frequency of fruit set was observed in crosses of J. mimosifolia × J. cuspidifolia, whereas very little fruit set was observed in the reciprocal cross (J. cuspidifolia × J. mimosifolia). Based on microscopic observations, pollen tubes penetrated the style and reached the ovary in crosses of J. mimosifolia × J. cuspidifolia. On the other hand, few pollen tubes reached the ovary in J. cuspidifolia × J. mimosifolia crosses. The germination rate of seeds obtained in crosses between J. mimosifolia × J. cuspidifolia was relatively high, whereas it was quite low in the seeds obtained from the reciprocal cross. All of the seedlings obtained from these interspecific crosses were confirmed as hybrids by isozyme analysis. Several characteristics of these hybrids and their parents were also investigated.