Abstract: Crossbreeding of Cycas revioluta X C. siamensis achieved successfully in 1986. Seven year monitoring to F1 growth carried out. Characteristics of the filial generations were as follows: stem covered with persistent petiole-bases; leaflets thin-coriaceous, the middle ones 12-15 cm long, 0.7-0.8 cm wide, spaced at 0.8-1.0 cm, slightly revolute at margin; petioles with many sharp spines on both sides.