Abstract: Combined with global climate change, ozone depletion and ocean acidification, marine plastic pollution has become a global environmental issue, among which marine micro/nano plastics have become the focus of attention. Compared with microplastics, nanoplastics have smaller particle size, larger specific surface area, higher environmental individual concentration, and are more readily to be ingested by marine organisms, causing stronger toxicity to marine organisms. Therefore, environmental effects of nanoplastics on the marine environment has become a research focus in the field of environmental science in recent years. However, so far, there is still a lack of systematic research and clear understanding of the environmental behavior and biological effects of marine nanoplastics. Therefore, this review summarized detection/analysis methods and environmental behavior of marine nanoplastics, analyzed the toxic effects of nanoplastics on marine organisms and their toxicity mechanisms, and proposed the research directions of marine nanoplastic environmental effects. Our review provides important basis for ecological risks evaluation of marine nanoplastics and an important reference for effectively dealing with ocean plastic pollution.