Microalgae have strong potential as novel sources of nutraceuticals, as they contain significant amounts of highly valuable bioactive compounds. This study focuses on the bioprospection of the microalga Isochrysis galbana biomass and its extracts (aqueous and ethanolic), determining total polyphenols, laminarin, fucoxanthin, coenzyme Q10, and -carotene contents, and also assessing several biological activities (antioxidant, cytotoxicity, and hypocholesterolemic). I. galbana exhibited high phenolic content, both on aqueous and ethanolic extracts. The microalgal freeze-dried biomass presented a low laminarin content, higher content of fucoxanthin (6.10 mg/g dw), and relevant β-carotene and Coenzyme Q10 contents were detected. I. galbana aqueous extracts presented a high antioxidant capacity (approximately 90 % inhibition by ABTS method). Furthermore, I. galbana biomass and ethanolic extract showed significant cytotoxicity against human HeLa cervical cancer cells, with IC50 values of 0.32 and 0.28 mg/ml respectively, demonstrating potential interest for further anticancer studies. The aqueous extract of I. galbana induced a significant decrease of cholesterol absorption through Caco-2 monolayers, modelling the human intestinal barrier, which suggests that it may contribute to decrease the dietary cholesterol absorption.