Monomeric bR was reconstituted into DMPC vesicles. Absorption spectrum and CD spectrum show bR molecules in DMPC vesicles were in monomeric state. We have measured the effect of pH gradient on photoelectric response of monomeric bR BLM. When the pH in inside container was higher than the pH in outside container and the difference of pH was more than 2, we have observed the change of polarity from positive to negative. Also we have discussed the reason of the change of polarity of photoelectric response.