Chronic diseases including cardiovascular diseases, type II diabetes and cancer have become worldwide health issues. Unhealthy lifestyle may aggravate inflammation of the system, which could be the main cause of chronic diseases such as cardiovascular disease and cancer. The purpose of this study was to investigate the potential health benefits of bioactive compounds extracted from Laminaria japonica to protect against different chronic diseases. Laminaria japonica is a famous type of brown algae, which is widely used with its outstanding health benefits. However, there is limited research studying about the health benefits of different bioactive extracts from Laminaria japonica. Here, the study was made up of two core contents to investigate the health effects of bioactive extracts from Laminaria japonica. First part focused on fat-soluble bioactive compounds, such as phenolic compounds, which were divided into extractable fraction and non-extractable fraction. They were studied on the anti-inflammatory and anti-cancer effects of cell culture study. The second part focused on water-soluble bioactive compounds, for instance, polysaccharides. They were extracted by polar solvents like water and were studied on the influences on human gut microbiota. Human gut microbiota is the system that various microorganisms, such as bacteria, archaea, and eukarya inhabiting the human gastrointestinal (GI) tract. Diet is one of the major factors to affect the composition of gut microbiota, which could further influence the effect of modulating immunity and preventing diseases. For the study of phenolic compounds, the results of TPC, FC and TC measurements revealed that the content of phenolic compounds in extractable fraction was higher than that in non-extractable fraction. The results of the measurement of anti-inflammatory effects in macrophages RAW 264.7 cells suggested that the inhibition capacity of extractable fractions to NO production induced by LPS was stronger than that of non- extractable fractions. However, the inhibition capacity of extractable fractions to the growth of human colon cancer cell HCT 116 was weaker than that of non-extractable fractions. Moreover, for the study of polysaccharides, during the experiment of in vitro fermentation to mimic GI tract, the polysaccharide of fraction C, alginate, was more effectively utilized, with the significant reduction of pH and total carbohydrate content. Overall, our results suggested compounds extracted from Laminaria japonica were bioactive and were potential to be developed as functional foods in the future.