The rambutan (Nephelium lappaceum L.) peels and its extract have been reported to contain bioactive compounds that promote fermentation inhibition activities. This research was aimed to investigate the rambutan peel and its extract as a potential natural fermentation inhibitor to inhibit alcohol fermentation in coconut (Cocos nucifera L.) sap for sugar production. Rambutan peels were prepared as size-reduced fresh rambutan peels and as extract of rambutan peels, which was obtained by maceration using ethyl acetate as solvent. The size-reduced rambutan peel with concentrations of 45, 50, and 55% (w/v, wb) and/or rambutan peel ethyl acetic extract with concentrations of 1, 2, 3, and 4% (w/v, db) were then applied to fresh coconut sap which was fermented for 7 days. Physicochemical properties of the sap including pH, total dissolved solids, total titratable acidity, total reducing sugar, total sugar and alcohol content were analyzed on day 0, 1, 2, 3, 4, 5, and 7, and microbial counts were determined on day 0, 1, 3, 5, and 7. The alcohol content of coconut saps treated with size-reduced rambutan peels with concentration 45, 50 and 55% on day seven (3.06±0.34%, 2.67±0.21%, and 2.33±0.07%, respectively) were significantly lower than control (4.40±0.39%), whereas the alcohol content of coconut sap treated with ethyl acetic rambutan peel extracts with concentration 1, 2, 3, and 4% on day seven (3.99±0.13%, 2.56±0.05%, 1.10±0.21%, and 1.12±0.06%, respectively were also significantly lower than control (6.00±0.44%). These results demonstrated that size-reduced peels and ethyl acetic rambutan peel extract successfully inhibited alcohol fermentation in coconut sap. In further study, coconut saps treated with size reduced peels and ethyl acetic peel extracts which were chosen based on their low alcohol content and high total sugar content during fermentation time, and were cooked into coconut sugar. Coconut sap treated with size-reduced peel 45% on day two exhibited the lowest total sugar content (24.27±0.79%) of the sugar product; coconut sap treated with ethyl acetic peel extracts 3% on day four exhibited the highest total sugar content (37.19±2.02%) of the sugar product, although this was still significantly lower than control (54.54±0.40%). Taken all together, it may be recommended that the sugar produced may be used for food products which are not intended as hard texture food