As an emerging two-dimensional layered material, black phosphorus nanosheets show unparalleled optical and electronic properties. Although black phosphorus nanosheets have attracted much attention in the photoelectric field, their applications in biomedical field were still limited due to their poor biocompatibility of current synthesis strategies. Herein, we propose a novel synthetic strategy for black phosphorus nanosheets that rely on Tween 20-assisted liquid exfoliation and post-processing in deoxygenated water. Microscopic and spectroscopic analysis suggested that the produced black phosphorus nanosheets dispersions exhibited good stability and higher yield compared with other currently prepared methods. Because of their ultrahigh exfoliation efficiency, the black phosphorus flakes present few-layer and even monolayer, which are thinner than the most dispersions of black phosphorus. Thus, this method enables mass-production of high-quality few-layer black phosphorus with high biocompatibility, and has the potential to be directly used in the biological field.