A binding strap used in connection with a SpO2 sensor comprises two clamping portions each of which is provided with an access opening for passing the light emitting portion or light receiving portion of the SpO2 sensor and a holding recess for holding corresponding light emitting portion or light receiving portion, wherein said access openings are designed to allow corresponding light emitting portion or light receiving portion to pass only when said access openings are undergoing a certain amount of deformation. The binding strap of the present invention is advantageous in that the light emitting portion and the light receiving portion of the SpO2 sensor might be tightly secured to the binding strap, and the lost of the binding strap when not use is ensured to be hard.