In order to screen new radical scavenging principle which is expected to be antiaging drug lead, we have investigated 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of the marine microalgae, greenalgae(10 speices), diatom (10 speices) and blue-green algae (10 speices). The significant activities$(IC_{50}:;<100;{mu}g/ml)$ were observed in 4 species of green algae (MA002, 006, 009, 010), 1 species of diatom (MA015) and 5 species of blue-green algae (MA017, 018, 019, 024, 025). Within the scope of family tested, MA009 $(IC_{50}:;=78;{mu}g/ml)$, MA015 $(IC_{50}:;=38;{mu}g/ml)$ and MA019 $(IC_{50}:;=41;{mu}g/ml)$ displayed the most significant activity. Among the marine microalgae tested at family level, cyanophycean blue-green algae was shown to be the most active family on screening of new bioactive compounds.