The micro-/nano-fiber (MNF) and plas tic optical fiber (POF) coupler were fabricate d directly from the commercial POF by heating and pulling method.The glucose solution is used as the refractive ind ex (RI) medium.The RI sensing properties of the ma cro-bending MNF are investigated and analyzed by measuring the optical output intensity of the MNF.The experimental results show that the macro-bending MNF i s sensitive to the low RI range of a liquid;the larger macro-bending radius of the MNF corresponds to a higher sensitivity;and for a fixed macro-bending ra dius,the MNF with a smaller fiber diameter has a higher sensitivity.With a fiber diameter of 25μm,the MNF has the highest RI resolution of 7.96×10－5 f or the RI range from 1.332to 1.391at the wavelength of 635nm.The MNF can be appl ied to the biological and chemical sensing fields with simple fabrication and hi gh sensitivity.