Precipitation of magnesium hydroxide using narrow channel reactors has been studied. Effects of channel dimensions (two square cross-sectional area channels with areas 1 and 2 mm(2)), type of mixer (Y and cross mixer), flow rate of the reaction mixture, and reaction parameters on the particle size and particle size distribution of magnesium hydroxide have been studied. Reaction parameters studied were the effect of the concentration of magnesium chloride, temperature, pH, and addition of the cation Al3+. Some tests were carried out in a stirred batch reactor for comparison with the narrow channel reactors. Comparison of mean particle size of the two reactors on a power consumption basis clearly indicates the superiority of the narrow channel reactor. The results clearly show that the narrow channel reactor is a much more compact process equipment having significantly lower capital and operating costs as compared to a conventional stirred reactor yielding simultaneously a better product. All these advantages lead to an intensified process.