Flax (Linum usitatissimum L.) is mostly grown in temperate climate conditions. The rising demand for natural fibres other than cotton has re-introduced flax cultivation in to the agenda. This situation has necessitated the acceleration of flax production research in Turkey. The purpose of this research is to discover the best seeding density for flax fibre cultivation. The trials were carried out with the Rolin flax variety at the coordinates 41°21′53″ N and 36°11′17″ E, during the winter seasons of 2018–2019 and 2019–2020, at densities of 500, 750, 1000, 1250, 1500, 1750, and 2000 plant m−2, by using a random block design. According to the results obtained from analysis of variance, where all these charectors examined viz, years, densities, year and density interaction were found statistically significant (p < 0.01). The highest straw, fiber and seed yields per decare were measured at 2000 plant m−2 density, while as the lowest values were determined at 500 plant m−2 density. However In the interaction of year and density, the highest plant height and technical length were measured in the first year at 1750 plant m−2 density at 102.7 cm and 80.2 cm, respectively. Similarly the highest straw yield (764 kg da−1), fiber yield (198.6 kg da−1) and seed yield (133.9 kg da−1) were measured in the first year at 2000 plant m−2 density. Adequate rainfall during the rapid development stage of winter flax in April-May boosted plant height, technical length, straw, seed, and fibre yield. Although the yields were low during the second year, which was dry. While the positive significant correlation (**; p < 0.01) was found between plant density and plant height (r = 0.907 **), straw yield per decare (r = 0.981 **), seed yield per decare (r = 0.973 **), fiber yield per decare (0.978 **), technical length (r = 0.828; * p < 0.05), negative significant correlation (p < 0.01) was found between plant density and the number of secondary branches (r = −0.955 **), stem diameter (−0.955 **) and plant seed weight (r = −0.923 **). According to the data recorded in two-years. It was observed that for high straw, fiber and seed yield, 2000 plant m−2 density was appropriate for cultivating flax fiber during the winter growing period in mild climate conditions.