The force required to disassemble block copolymer micelles in water has been directly investigated via atomic force microscopy-based single-molecule force spectroscopy. The force needed to disassemble block copolymer micelles of poly(acrylic acid)-polyfluorene-poly(acrylic acid) in water is found to be 23 pN. The force increases as the stretching velocity increases, indicating that micelle disassembly is a dynamic process. In addition, the disassembly force is sensitive to the properties of the solvents. This study represents the first attempt to employ single-molecule force spectroscopy to directly measure the force needed to disassemble block copolymer micelles in water.