In the present work the photo responses of bacteriorhodopsin in purple membrane fragments were studied under continuous high intensity light illumination in different ranges of pH, temperature and ionic strength. The activity of bacteriorhodopsin was measured as pH vs. time by using a combined pH electrode, The activity of the bacteriorhodopsin in purple membrane fragments at acidic pH was found to be more sensitive to temperature changes than it was at physiological or higher pH values. The activity of bacteriorhodopsin was also found to be the function of varing concentrations of different salts. The kinetic analyses of light reactions (proton dissociation) and dark reactions (proton association) were carried out at different pH, temperature and ionic strengths, The kinetic data revealed that the proton dissociation in the light and proton association in the dark followed the first order kinetics in the pH range of 6.7-7.2 at room temperature, Beyond these limits the kinetic behavior of bacteriorhodopsin was found to be much more complex.