Rambai (Baccaureamotleyana(Müll.Arg.) Müll.Arg.) is an underutilized fruit tree from Indonesia.The growth and developmental stages of the rambai fruit are not well characterized.This study aimed to investigate the flowering phenology and fruit development of rambai at the Mekarsari Fruit Garden, Bogor (Indonesia),fromJune 2019 to July 2020.Four trees were used in this study, and ten panicles from each tree were labeled as samples.The results of the study revealed that therambai fruit undergoes five stages of phenological development: flower initiation, flower differentiation, anthesis, fruit development, and fruit ripening, which occurred at 0, 14, 21, 91, and 117 days after panicle shoot appearance, respectively.The ripening stage required the longest duration (117 days after the appearance of the panicle shoot) and largest thermal units (2108.5°C days).The fruit is predicted to be physiologically ripe at 14 weeks after anthesis, and the peel and fruit turned yellowish-green and became softthen.After ripening, the fruit had the highest level of sweetness, with total soluble solids up to 12–18 °Brix and a total titratable acid contentof 3.5–5%.