Carotenoids which are important towards the biological activities are produced by all higher plants, some bacteria and algae. Marine microalgae can produce a variety of substances including carotenoids and it has a commercial interest as production of microalgae in controlled condition is affordable. Three species of marine microalgae; Chlorella sp., Dunaliella sp. and Isochrysis sp. were cultured and carotenoids were extracted for testing. The total carotenoid present in dry weight of Chlorella sp., Dunaliella sp. and Isochrysis sp. were 55.1%, 99.3% and 29.4% respectively. The carotenoids from the microalgae were tested for toxicity level against MCF7 cancer cells, with Chlorella sp., Dunaliella sp. and Isochrysis sp. showing IC50 value 0.25mg/ml, 0.3 mg/ml and 0.32 mg/ml from crude extract respectively. Antioxidant di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH) scavenging activity were present in all the three types of microalgae. In-vivo gastritis studies on model mice showed healed result from Dunaliella sp. but not from Chlorella sp. and Isochrysis sp. From the three microalgae species, Dunaliella sp. has the highest ability to promote gastric healing as it contains antioxidant and antimicrobial properties.