Ripe Rhizophora mucronata has been consumed by mangrove society in Indonesia. The aim of the research was to study the potency of ripe R. mucronata fruit flour, reducing blood glucose level in Alloxan-induced diabetic rats. Ripe R. mucronata fruit flour was administrated to Alloxan (125 mg/kg body weight)-induced diabetic male Wistar rats at different doses (500, 1000, 1500 and 2000 mg/day/head) for 18 days and a positive control group given standard drug for diabetic (glibenclamide 0.09 mg/day/200 g body weight). The result showed blood glucose level of negative control groups increased, whereas positive control group and experimental rats group fed flour of mangrove fruit significantly declined. Ripe of mangrove fruit flour at doses 1000, 1500, 2000 mg/day/head body weight indicated similar effect to glibenclamid in decreasing blood glucose level. The potency of ripe R. mucronata fruit flour as antidiabetic related to the phytochemical compounds of its such as tannins, saponins, flavonoids, and steroid. Ripe R. mucronata fruit flour contained 7.50% soluble dietary fiber and 38.60% insoluble dietary fiber. Thus the ripe R.mucronata fruit flour is a candidate as functional food source especially antidiabetic.