ABSTRACT   Two field experiments were conducted during the two successive seasons 2007/2008 and 2008/2009 at Sakha Agric. Res. Station, Kafr El-Sheikh Governorate to study the effect of four harvesting dates i.e. 135, 145, 155 and 165 days after sowing on yield and its quality of six flax genotypes namely, Sakha1, Sakha 2, Sakha 3 and Giza 9 varieties and two new promising strains (strain 16 and strain 22). This study was laid out in a split-plot design, with four replications, the main plots were allocated to the six flax genotypes, whereas, the sub-plots contained the harvesting dates. The obtained results could be summarized as follow:       Sakha 3 and Giza 9 varieties gave the highest means for technical length, fiber yield/plant as well as per fed., fiber length, fiber percentage, fiber strength, fiber fineness, germination % and crude protein %, whereas strain 22 (yellow seed) surpassed the other flax genotypes which produced the highest values for No. of seeds/plants, seed yield/fed., oil content and oil yield/fed.      The harvest date of 155 days after sowing showed significant increases in stem diameter, straw yield/plant as well as per fed. fiber yield and its quality and crude protein % compared to the other three dates (135, 145 and 165 days after sowing). However, delayed harvesting date to 165 days after sowing recorded significant increase in technical length, upper branching zone length, seed yield and its related characters, germination %, seedling vigour, seed index, volume of 1000-seed, oil content and oil yield/fed. The interactions among the studied factors had significant effects on straw yield/fed., No. of capsules/plants, fiber strength and germination % in the first season of study, while the characters of the upper branching zone length, seed yield/fed., oil yield/fed., fiber length and oil content in both seasons.