TheJ‐aggregates with variation of size of 3,3’‐disulfopropyl‐5,5’‐dichloro‐9‐ethyl‐thiacarbocyanine (Dye 1) were formed on the surface of octahedral AgBr microcrystals in a photographic emulsion, and their size was evaluated by a spectroscopic method. Light‐induced electron transfer from the aggregates to the microcrystals left positive holes in the aggregates, which gave rise to an electron‐spin resonance (ESR) signal. The intensity of the ESR signal increased, and the rate of its decay decreased, as the aggregate size increased. The decay of the signal was caused by the recombination of positive holes with photolytic silver clusters after repetition of detrapping and trapping of positive holes by the aggregates. The enthalpy of activation of the decay, for which the detrapping of positive holes was responsible, was independent of the aggregate size. The analysis of the saturation of the signal intensity with increasing the power of microwave has indicated that the increase in the aggregate size could enhance the migration and thus increase the entropy of positive holes in the aggregates. It is therefore considered that the decrease in the rate of the decay of positive holes with increasing the aggregate size resulted from the change, not in the enthalpy, but in the entropy of positive holes in the aggregates. The above‐stated behavior of positive holes in the aggregates gave an explanation for the insufficiency in photographic sensitivity caused by the growth ofJ‐aggregates of Dye 1.