Carbon dots (CDs) synthesized from natural organic precursors, such as glucose, citric acid, glycerol, and chitosan, have attracted great interest since natural organic precursors provide abundant carbon sources, a variety of heteroatoms for doping (such as N, S, and P) and good biocompatibility. However, previous approaches utilized organic solvents during synthesis procedures, which limited their widespread development in biomedical applications. Herein, the facile synthesis of a new type of bright CDs through an eco-friendly method that employs linseed as a natural precursor has been reported. The as-obtained CDs possessed high quantum yield of 14.2%, excellent solubility and photostability as well as excitation-dependent photoluminescence (PL). In addition, the as-prepared CDs exhibited great potential in cell imaging owing to negligible cytotoxicity as well as excellent biocompatibility and great resistance to photobleaching. Subsequently, the as-prepared CDs were also applied in the fabrication of a biosensor for sensitive detection of butyrylcholinesterase (BChE) based on the fluorescence quenching mechanism, which could be used as an indicator for detecting pesticides and nerve gases. By monitoring the change in the fluorescence intensity of the CDs, the activity of BChE was sensitively analyzed. The limit of detection (LOD) of BChE was 0.035 mU mL-1. The as-prepared CDs have potential applications in both biosensors and bio-imaging.