Abstract. Majumder S, Acharyya S, Ghosh A, Chakraborty S, Sarkar S, Saha S, Bhattacharya M. 2021. Insights into low biological activity of wax apple (Syzygium samarangense) juice by in vitro phytochemical investigation with special reference to metabolomics. Biofarmasi J Nat Prod Biochem 19: 30-37. Wax-apple (Syzygium samarangense) is an Asian waxy and juicy fruit reported as antidiarrheal and useful in diseases like dysentery. Moreover, no stronger medicinal evidence has been found associated with this fruit and its juice to ensure more biological activities and composition. Being edible, waxy, and juicy, this fruit is quite popular in coastal areas and islands. Still, the absence of stronger medicinal and biochemical evidence associated with this fruit or its juice has created a worldwide underutilizing status. In this research, we intended to investigate this fruit juice's phytochemical characteristics and composition through detailed biochemical tests and metabolomics. Qualitative detection tests for bioactive groups of molecules (tannin, coumarin, cardiac glycosides, terpenoids, flavonoids, phenol, etc.), antioxidant assay, and antibacterial test simply showed its low in vitro biological activity. GC-MS-based metabolomics was performed where the presence of wax components like long-chain hydrocarbons was revealed. Based on the GC-MS-based metabolomics, a proposed pathway of wax apple's wax biosynthesis has been established. The overall study strongly clarified the absence of bioactive components in this fruit. It proved that the fruit, named wax apple, is actually a source of natural waxes that can be responsible for its claimed antidiarrheal property.