The objective of this work is using the online measurement method to study the process of precipitation of nickel hydroxide in a single-feed semi-batch stirred reactor with an internal diameter of D = 240 mm. The effects of impeller speed, impeller type, impeller diameter and feed location on the mean particle size d(43) and particle size distribution (PSD) were investigated. d(43) and PSD were measured online using a Malvern Insitec Liquid Process Sizer every 20 s. It was found that d(43) varied between 13 mu m and 26 mu m under different operating conditions, and it decreased with increasing impeller diameter. When feeding at the off-bottom distance of D/2 under lower impeller speeds, d(43) was significantly smaller than that at D/3. PSDs were slightly influenced by operating conditions. (C) 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.