Abstract: One of the most important conditions for preparation of “ultra fine” solid particles by precipitation is high and uniform supersaturation. Based on investigations into impinging streams, a submerged circulative impinging stream reactor (SCISR) has been developed, which has the special flow configuration of circulating perfect mixing flow-non-mixing flow in series and promotes micromixing strongly in the impingement zone. The impingement zone can create high and uniform supersaturation environment for precipitation to yield nuclei in a huge amount, while the non mixing regions with much lower supersaturation favor deactivation of micro-crystal surfaces. The preparation of “ultra fine” white carbon black by the common precipitation process is studied experimentally with SCISR, and the optimal operating conditions are obtained. The SCISR can be operated both in batch and continuously for the mentioned process. An investigation is also made for comparison between performances of SCISR and stirred tank reactor (STR) in the preparation of white carbon black, both operated in batch. The products of SCISR have the sizes ranged from 0.5 μm to 2.0 μm with the averages of 1.1—1.6 μm, which are finer with narrower size distribution than those from STR. The results of the experiments on spray drying of the reacted materials show that the products from SCISR are stable in size, suggesting no agglomeration of micro particles during the treatment after reaction.