Five commercial cotton cultivars of the two Egyptian cotton cat­egories, i.e., Extra-long staple (Giza 76, Giza 77 and Giza 70) and long-staple cottons (Giza 75 and Giza 80) were used in this study. From each cultivar, samples of fibers of three levels of micronaire reading (low, medium and high) were obtained and subjected to four different temper­ature treatments (0, 50, 100 and 200oC). The results obtained showed that reflectance percent (Rd%), fi­ber length at both 50% and 2.5% S.L., fiber strength at zero and 1/8 gauge length, fiber strength, uniformity ratio, fiber elongation and fiber wax content were significantly decreased as the temperature degrees in­creased while; degree of yellowness (+b) and fiber sugar content were significantly increased. The severe effect of different temperature treat­ments were more pronounced on cotton fibers of low micronaire read­ing. Fiber length uniformity ratio did not follow a constant trend of in­creasing or decreasing. Micronaire reading was not affected by different temperature treatments.