This study presents a research of klampok watu plant (Syzygium littorale) including the Myrtaceae family. As far, only a few report about Syzygium littorale in leaves, fruit, stem bark or other parts. The stem bark of plant was extracted with an organic solvent and then fractionated (isolated) using standard chromatographic techniques. The molecular structure of pure isolates was elucidated and identified with spectroscopic evidence and compared to literature data and authentic sample. The dry powder of the stem bark was extracted with methanol and partitioned with chloroform and hexane, respectively. Isolation of the methanol fraction through vacuum liquid chromatography and followed by recrystallization which always monitored by TLC, yielded a pure compound. The identification result of pure compound showed there are palmitic acid and pinostrobin. The finding of the compounds from the plant is for the first time, although it have previously been found in other Syzygium plants, such as S. samarangense, S. cumini, S. polyanthum, S. polycephalum, etc. The methanol fraction, the isolated compounds palmitic acid, pinostrobin, and vitamin C showed antioxidant activity with IC50 value of 44.85; 189.9; 184.88, and 11.81 μg/mL, respectively.