Technical Abstract: Cotton fiber quality is important in the textile industry to meet high-speed automation in the new century. Improvement of fiber quality requires better understanding of genetics of fiber quality properties. We conducted large experiments that included eight crosses from five cotton parents with different fiber strength measurements. Fiber strength of the segregating progeny was measured individually and the data were subjected to analysis of a genetics model that mixed major genes and minor genes. The results showed that in all fiber quality properties there was at least one major gene plus some minor genes. The major gene contributed the improvement 19.6% fiber strength, 13.9% fiber length, and 32.0% fiber fineness, for example, in one cross of two Upland cottons with high (7235) and low (TM-1) fiber strength.