It had been found that developing agents do not affect the rate of fixation in monobaths of higher pH (above 11) but most of them slow down it in those of relatively lower pH, as shown in our previous reports. The mechanisum of the retardatory effect of developing agents on the rate of fixation at relatively lower pH were investigated in this paper. The results from some experiments relating to the retardatory effect of developing agents on the fixation process showed that it is caused by decrease in the rate of diffusion of the fixing agent and the complex silver-bearing ion through the emulsion layer due to adsorption of undissociated developing agents having hydroxyl groups on gelatin.