Abstract: An effective method for measuring activity of starch branching enzyme was developed in this study. Tuberous roots of mature cassava were collected as materials to study various reaction parameters of the starch branching enzyme (SBE), including extracting solution of enzyme, enzyme concentration, reaction system, reaction duration and termination methods. Finally, we introduced an improved method for detecting activity of cassava starch branching enzyme. Firstly, 0.5 g root of mature cassava was ground into pulp with extracting solution. Then, the crude enzyme solution was obtained from the supernatant after centrifugation. The crude enzyme solution was diluted and added with 0.5% soluble starch at 37℃ water bath for 10 min. Then, the reaction was terminated by boiling water. Iodine solution and KI were added to conduct chromogenic reaction for 10 min. The activity of enzyme was measured at 660 nm. One unit of cassava SBE activity was defined as the amount of substrate causing 1% decrease in absorbance of iodine blue at 660 nm. The improved method is simple and rapid for measuring activity of starch branching enzyme from different cassava germplasms with excellent repeatability.