The relation between cotton fiber properties and dye-ability has been studied for eight Egyptian cotton varieties representing a wide range of fiber properties grown during four successive seasons. The dye-ability was studied for both mercerized and un-mercerized cotton samples. A relationship was found to exist between dye absorption, chemical activity (accessibility %) and fiber maturity% of the commercial Egyptian cottons. These studies indicate that there is a strong correlation between fiber maturity, accessibility and dye-ability at equilibrium. The results obtained showed that the dye-ability of the mercerized cotton varieties had the highest values than the un-mercerized cottons due to the chemical and physical structure of the fibers. The cotton fibers have a natural porosity consisting of pores and micro capillaries whose accessibility can increase. Mercerized Egyptian cotton fibers are more absorbent and have greater affinity for dyestuff. The results obtained revealed that dye uptake increased gradually in the Egyptian cotton with increasing fiber maturity %.