Abstract: Phenology is the study of the timing of recurring biological events in plant and animal world, especially with regard to seasonal and interannual variations in climate, as well as habitat factors. Phenological study of Delonix regia (Boj.) Raf. occurring in Onitsha with a tropical dry deciduous vegetation was carried out to collect information about the different phenological phases of the tree. The early to late stages of four phenophases, leafing, flowering, fruiting and ripening were observed and recorded once in every two weeks for a yearly cycle. Two-digit codes were used for inclusion of the principal growth stages and the secondary growth stages, and these defined the phenological phases observed. The results showed that changes in the prevailing seasons influenced the leafing and flowering phenology in D. regia. Flowering phenology started soon after the tree had resumed leafing with the early rains in the rainy season. Leafing, flowering and fruiting phenology started at different time periods and peaked synchronously. Also, the result showed that deciduousness in D. regia started with the onset of dry season in November and ended shortly before the rains in February. In addition, the study has provided baseline information on the phenology of D. regia, and this will, in the future, serve as a correlation between phenology and climate change in the area. Thus, it is suggested that functional and effective meteorological station be established in the area for integration of climatic records.