The abnormal accumulation of iron in the brain has been suggested to be toxic to neuronal cells and proposed as a possible cause of neurodegenerative disorders. Particularly, studies on the pathogenesis of neurodegenerative diseases have suggested that the excessive accumulation of iron in the specific brain regions may be responsible for neurodegenerative changes associated with the pathogenesis of Alzheimer's, Parkinson's, and Huntington's diseases. As a part of studies searching for natural substances protecting neuronal cells against the iron-evoked toxic injury, an aqueous extract containing the non-protein components of the cyanobacterium Arthrospira (Spirulina) platensis, designated "the protein-deprived extract", was prepared, and its effect on the iron-evoked damage to PC12 cells was examined in an in vitro model experiment. The protein-deprived extract caused a protective effect against the iron-evoked damage to PC12 cells as a consequence of preventing the free radical-evoked DNA degradation. Further studies showed that the extract has antioxidant and free radical-scavenging activities, which might be based on polyphenolic compounds in the extract. Thus, polyphenolic compounds contained in A. platensis are suggested to be potentially active substances responsible for the protective effect of Arthrospira extract against the iron-evoked neurotoxicity and possibly for the protection of neurodegenerative disorders induced by excessive iron accumulation in the brain.