Type 2 diabetes is a global health problem with increasing prevalence related to several conditions; one of these is due to obesity. Rambutan (Nephelium lappaceum L) seeds contain various phenolic compounds. The present study was designed to evaluate the phytochemical content and the inhibitory potential of rambutan seeds extract and fractions on glucose-6-phosphate dehydrogenase (G6PDH), α-glucosidase, and triglyceride activities ex vivo in 3T3-L1 cell line (pre-adipocytes) for an antidiabetic and antidiapogenesis agent screening. Phytochemical analysis was performed using modified Farnsworth method. Cytotoxicity or cell viability of rambutan seed extracts (distillated ethanol 70%) and fractions (hexane, ethyl acetate, butanol, and water fractions) were assayed using 3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. Triglyceride (TG) level, G6PDH and α-glucosidase activity and inhibitory activities were determined by commercial assay kits. Extract and fractions of rambutan seed contained alkaloid, terpenoid, triterpenoid, and phenol; flavonoid, tannin, saponin, and steroid were undetected. The lowest cytotoxic activity and safe substances on 3T3-L1 cell were rambutan seed extract and hexane fraction. Rambutan seed extract at the dose of 50 µg/ml was the most active to lower G6PDH and α-glucosidase as well as TG level. Rambutan seed extract and hexane fraction have the phytochemical bioactive content to possess inhibitory potential on G6PDH and α-glucosidase as well as TG level in the present experimental set of 3T3-L1 cell lines.