The present paper established new methods for determining the activities of starch branching enzyme (BE) and starch synthase (SS). The methods are based on the calculation of the data on chain-length distribution obtained from the fluorophore-assisted carbohydrate capillary electrophoresis (FACE) method, in which the molar percentage of each linear chain comprising the branched glucan can be precisely determined. The FACE method can give us two important results at the same time, namely the chain-length distribution and the enzyme activity, for characterization of BE and SS. Although the activity of BE has been quantitatively determined by measuring the reducing power of the isoamylorysates of the reaction product and the substrate, this method has difficulties in having a high background value when branched glucan such as amylopectin and glycogen is used as substrate in the in vitro reaction, whereas the FACE method has no such disadvantages.