Abstract: Data from 12 F1s combinations of G. hirsutum L. × G .barbadense L. and 3 G.Barbadense L. varieties in 2003 and 89 BC2F1 lines of G. hirsutum L. × G .barbadense L. with the G. hirsutum L. as recurrent parent in 2005 were analyzed to estimate the differences of fiber quality traits between naturally open bolls and big bolls at frost season. The results showed that there were significant differences of -1.15mm, -1.00 and -2.16 in difference values of the mean of fiber length, micronaire and uniformity respectively, between big bolls at frost season and naturally open bolls from 12 F1s combinations of G. hirsutum L. × G .barbadense L. and 3 G.Barbadense L. varieties in 2003, and no significant difference for fiber strength and elongation. And there were significant differences of +1.73cN/tex, -1.33, -0.49 and +0.21 in difference values of the mean of fiber strength, micronaire, uniformity and elongation respectively, between big bolls at frost season and naturally open bolls, for 89 BC2F1 lines of G. hirsutum L. × G .barbadense L. in 2005, except no significant difference for length. The results indicated that there existed significant or extremely significant positive correlation for all fiber quality traits between big bolls at frost season and naturally open bolls, and it were similar for histograms of all fiber quality traits between big bolls at frost season and naturally open bolls in 2003 and 2005. So, some of fiber quality traits, especially micronaire and uniformity, were prominently affected by the environment, but genetic difference of fiber quality traits among materials could be still reflected from big bolls at frost season, which was same as that of naturally open bolls. It was extremely important for fiber quality heredity and breeding selection of hybrid offspring of G. hirsutum L. × G .barbadense L..