The research aimed to find out the content of active compound of simplicia and the ability of methanol extract of Gracilaria salicornia, Halimeda gracilis, Halimeda macroloba, and Hypnea asperi as the antioxidant. Phytochemical testing of macro algae simplicia was conducted qualitatively to determine the presence of the active compound, i.e. phenolic, flavonoids, tanin, saponin, steroid, triterpenoid, alkaloid, and hidroquinon. The test method of antioxidant activity is the capture of free radical 1,1-Diphenyl-2-Picrylhidrazyl (DPPH). The active compounds which belongs to macro algae that are tested are flavonoids, steroids, and saponins. The results of examination of antioxidant activity showed the highest percentage of free radical capture of DPPH methanol extract of G. salicornia was 7,228%. The result of univariate ANOVA in antioxidant activity, indicating that there was an effect of concentration on free radical capture of DPPH (p ≤ 0,05) and did not show the interaction between species of macro algae and concentration. The highest percentage of interception DPPH free radical of methanol extracts of each macro algae tested i.e. G. salicornia, H. asperi, H. gracilis, and H. Macroloba respectively