Abstract: The distribution of 14C-assimilates and the activity of starch synthetase during the grain filling period in wheat treated with 0.25% CCC were determined. The results showed that treatment with CCC at tillering stage influenced the distribution pattern of 14C-assimilates and the activity of starch synthetase differently at different stages of the grain filling period. Application of CCC retarded the movement of 14C into the grain and reduced the incorporation of 14C into the acid hydrolyzable fraction of the grain at the early stage but accelerated both of them at the later stage of grain filling period. Assays of starch synthetase activity indicated that CCC inhibited the activity of the enzyme at the early stage but promoted its activity at the later stage of the grain filling period. The significance of these findings is discussed in relation to the increase in sink capacity of the grain and to the increase in grain weight.