Confined impinging jet reactor (CIJR) offers advantages for chemical rapid processes and has become an important new reactor used in the chemical industry. The micromixing efficiency in a T-shaped CIJR for two tubes of inner diameter of 3 mm was studied by using a parallel competing iodide-iodate reaction as the working system. In this work, the effects of different operating conditions, such as impinging velocity and acid concentration, on segregation index were investigated. In addition, the effects of the inner nozzles diameter and the distance L between the jet axis and the top wall of the mixing chamber on the micromixing efficiency were also considered. It is concluded that the best range of L in this CIJR is 6.5-12.5 mm. Based on the incorporation model, the estimated minimum micromixing time t(m) of CIJR approximately equals to 2 x 10(-4) s. These experimental results indicate clearly that CIJR possesses a much better micromixing performance compared with the conventional stirred tank (micromixing time of 2 x 10(-3) to 2 x 10(-2) s). Hence, it can be envisioned that CIJR has more promising applications in various industrial processes. (C) 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.