The present study was carried out in the Laboratories of Cotton Technology Research Division, Cotton Research Institute, AgriculturalResearchCenter, to study the relationship between fiber properties and yarn properties and the contribution of fiber properties on yarn properties of some Egyptian cotton varieties. A bulk sample was taken from the cotton crop of 2005 season. Six Long-staple commercial cotton varieties namely, Giza 85, Giza 86, Giza 89, Giza 80, Giza 83, Giza 90 and promising cross ( Giza 89 x Giza 86) were used as experimental materials. These samples were spun into a constant carded yarn count 60'ѕ at twist factor 3,6. Fiber and yarn tests were carried out under the controlled atmospheric condition of 65 % ± 2 relative humidity and 21˚C ± 2 temperature. The simple analysis of variance, correlation and stepwise statistical technique were used. The obtained results revealed that all fiber and yarn properties under study were significant affecting with the varieties under study. Strongly positive significant correlation was found between single yarn strength and fiber strength. The positive significant correlation was found between fiber elongation and Single yarn elongation. Fiber fineness contribute better than fiber strength and consequently, yarn strength. Micronaire reading appears to have the most effect of any other fiber property on yarn irregularity. The best characters affecting yarn strength in Egyptian cotton grown at upper and delta region Egyptian long staple cotton varieties were fineness and CV % irregularity, while in lea count were fineness and maturity.