Three methods were used to determine the tannins content in cotton plant tssues. The tannin content in different organs and terminal leaves of four cotton varieties at different growth stages determined by the Folin's assay was nearly two folds as much as that determined by acid butanol assay, indicating that the Folin's assay only offers the total phenol content, but is not suitable for determining the content of condensed tannin in cotton. There was no significant difference between the results of vanillin assay and acid butanol assay, and hence, it is feasible to use vanillin assay to test the tannin content in cotton. Determinations at boll stage showed that the content of condensed tannin in calyx, boll shell and leaf was rather high, generally up to 5-10%, while that in petal, stigma, ovary and inner boll was lower (about 2%). The condensed tannin content in terminal leaf continually increased from seedling(< 1%) to boll stage (10% or so), indicating that the increased tannin content is closely related to the maturity, decrepitude and lignification of cotton tissues.