Appropriate plant densities is a key for maximizing flax productivity due to its main role in fixing energy. Two field experiments were conducted at the Experimental Farm of Gemmeiza Agriculture Research Station, Agricultural Research Center (ARC), Egypt, during the growing seasons of 2011/2012 and 2012/2013 to study the response of some fax genotypes; Sakha 3, Giza 10, strain 22 and Sakha 2 to different plant densities;                1500, 2000, 2500 and 3000 plants/m² and their effect on seed and long fiber yields and its components. The experiments were carried out in a split-plot design with three replications. The main-plots were assigned to flax genotypes. The sub-plots were allocated to plant densities. The results showed that the studied flax genotypes significantly differed in all studied characters in both seasons, except number of fruiting branches in the first season only. Using flax plant density of 2500 plants/m² significantly recorded the highest values of all studied characters, followed by flax plant density of 2000 plants/m², then 1500 plants/m² and lastly 3000 plants/m² in both seasons. It could be concluded that planting the genotypes Giza 10 and Strain 22 with plant density 2500 plants/m² in order to maximize straw and seed yields per feddan. While, for obtaining higher long fiber yield/fed, planting Sakha 3 cultivar with plant density 2500 plants/m² under the environmental conditions of Gemmeiza district, El-Gharbia Governorate.