Abstract : Seagrass is rich of marine resources and capable of producing secondary metabolites so that it can be used as functional food. Secondary metabolites that are generally produced by organisms play a role in self-defense from the environment or from the attack of other organisms including attached organisms/ epiphytes and prevent infection from pathogens and can be used as antioxidants. This study aims to analyze the content of bioactive compounds and the potential of antioxidant activity of Thalassia hemprichii extract. The examination of bioactive compounds is using phytochemical tests and examination of antioxidant activity is using the diphenylpicrylhydrazil (DPPH) method. Phytochemical test results showed that Thalassia hemprichii extract contained bioactive compounds in the form of flavonoids, saponins, tannins and polyphenols. The results of the antioxidant activity test of Thalassia hemprichii extract obtained IC50 values of 80.0331 indicating that Thalassia hemprichii extract has strong antioxidant activity. This research proves that Thalassia hemprichii contains bioactive compounds that have the potential to be antibacterial and antioxidant.