Cotton strength was measured at constant rates of extension with a universal tensile testing instrument to determine the effect of extension speed on the measurement of cotton strength. Extension speeds from 0.4 to 50.0 cm/min were investigated. The strength of fifty four cottons (including eighteen varieties from thirteen states) decreased slightly (0.42 gf/tex) at a high rate. There was considerable variation in the amount of strength loss among individual cottons. Neither cotton variety nor growth area appeared to be conclusive factors causing the loss.