In the present study, the effect of different immiscible additives on the reactive crystallization of a benzoic acid derivative from aqueous solution was investigated using the batch operation mode. Monochlorobenzene was used as the main additive, the effects of which on the crystal size distribution, shape and filterability of the crystal end-product were studied. The other immiscible additives studied here were toluene and hexane. The comparison between the studied additives was based on the obtained crystal size distribution. The experimental results of the crystal size distribution showed that monochlorobenzene and toluene were the compounds that resulted in a larger mean particle size. A microscopic study showed that the mean size increased due to the agglomeration of benzoic acid derivative crystals. Furthermore, the influence of the operating conditions, such as the now rate of the reactant, mixing intensity and initial concentration, on the crystal size distribution was studied. In the presence of monochlorobenzene, the operating conditions affected the crystal size distribution, whereas without the additive, their influence could be ignored. The mechanism of the additive effect is discussed here.