Zhongmian 42 and Xinluzao 36 were used as raw materials to determine the contents of soluble sugar and protein, as well as dynamic changes of enzyme activities after flowering during cotton fiber growth. The results showed that contents of soluble protein in the two species sharply declined 7 to 21 days after flowering, as the soluble sugar in Zhongmian 42 leveling off after 21 days of flowering while the soluble sugar in Xinluzao 36 dropped notably after 21 days of flowering before remaining stable after seven days later. The soluble sugar decreased 7 to 14 days after flowering before sharply rising to the maximum seven days later, and then began to decline quickly. The soluble sugar was the minimum after 35 days of flowering and then remaining stable. Peroxidase activity generally increased. Indole-3- acetic acid oxidase activities were low at 7 days after flowering. IAAO activity reached to the peaks on the 14th and 28th day after flowering. IAAO activity of two varieties decreased with the same trend 35 days after flowering.
