3-Methylpyridine-N-oxide is an essential intermediate in the preparation of 2-chloro-5-methylpyridine, which can be used to synthesize nicotine insecticides such as imidacloprid and acetamiprid. The traditional method of production of 3-methylpyridine-N-oxide is catalytic oxidation of 3-methylpyridine in semi-batch reactors. Due to strong exothermic reaction and explosive property of 3-methylpyridine, the reaction efficiency and safety is low using batch technology. Therefore, the development of a safer and efficient 3-methylpyridine-N-oxide production process is very necessary in industrial production. In this paper, microreaction systems were introduced into the preparation of 3-methylpyridine-N-oxide. The comparison of three different methods (traditional semi-batch method, co-current microreaction method, and circular microreaction method) showed that the circular microreaction method was the most applicable, with relative higher product yield (similar to 90%), less side reaction and better reaction control. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All lights reserved.