The present study was conducted to investigate the role of cot­ton varieties and lint grades as determinants of the major fiber chemical constituents of Egyptian cotton. The material used to carry out the Study comprised the 3 extra-long staple (ELS) varieties Gin 45, Giza 70 and Giza 88 together with the 3 long staple (1.8) varieties Giza 80. Giza 83 and Giza 89. Within each of the aforementioned varieties, the 4 lint cotton grades FG, 0, FGF and GF were used. The results obtained from this study showed that in the Egyptian cotton, the varietal differences in fiber chemical constituents were well established. However, Gin 83 variety attained the highest value of total reducing sugar content, Giza 89 had the highest cellulose content , while Giza 80 gave the highest values of both wax and ash contents. On the other hand, the least values of cellulose, wax, total reducing sugar and ash contents, were found in Giza 80, Giza 70 and Giza 89 varieties, re­spectively. Furthermore , lint grades which denote different levels of quality within a single variety, showed a consistent pattern of decrease in cellulose content and micronaire reading with lowering of the grade. Conversely, there was a general tendency of increase in wax total re­ducing sugar and ash contents as the grade of cotton declined. The analysis of variance evidenced that the variation in the chem­ical characteristics of cotton fibers, due to diversification of lint grades was markedly higher than that brought about by cotton varieties. Thus, it was concluded that, the impact of grades having different levels of quality is ascribed mainly to the effect of environmental conditions main­ly fiber maturity, on fiber chemical constituents, was obviously higher than that attributed to cotton varieties having different genotypes. Fur­thermore, significant interaction between cotton varieties and lint grades was found to effect on fiber chemical characteristics, indicating that the variability in chemical constituents, within each variety, due to the alter­ation of lint grade differed from one variety to another.