ObjectiveTo compare the in vitro antioxidant capacity of a diatom, Chaetoceros calcitrans (C. calcitrans) extracted using six types of solvents.MethodsEach extract was evaluated in terms of extraction yield, total carotenoid, fucoxanthin content, total phenolic and antioxidant capacities (DPPH and ABTS+ scavenging activity and iron chelating activity).ResultsThe methanol extract exhibited the highest yield [(22.71 ± 0.96) g/100 g dry weight (DW)], total carotenoid [(4.46 ± 0.36) mg/g DW], total phenolic [(2.49 ± 0.08) mg gallic acid equivalents/g DW] and second highest fucoxanthin content [(2.08 ± 0.03) mg fucoxanthin/g DW] as compared to other solvent extracts. Methanolic extract also exhibited significantly higher (P < 0.05) scavenging (DPPH, ABTS+) and iron chelating activities.ConclusionsMethanol was the recommended solvent for the production of antioxidant rich extract from C. calcitrans. Both carotenoids and phenolic acids were found to be positively correlated to the antioxidant capacities of C. calcitrans. Lead bioactives confirmed by subsequent high performance liquid chromatography studies were fucoxanthin, gallic acid and protocatechuic acid