The effect of different sowing dates on growth, development, morphological characteristics, yield, oil content and fatty acid composition of Linum usitatissimum L. was evaluated in semi-arid condition of Iran. An field experiment was performed in the basic of randomized complete blocks design with three replications for 6 sowing dates including (March 3, March 19, April 1, April 17, May 2, May 18). Our findings showed that sowing dates had significant effect on all morphological characteristics except thousand seed weight and oil percentage. An earlier sowing date led to better results. GC analyses revealed five fatty acids which linolenic acid was a major compound. Delaying in sowing decreased the linoleic and linolenic acid content but increased the palmitic and oleic acids. For the best production and fatty acid contents, it is postulated that the sowing date offers a high economic yield and oil quality. In conclusion, plants sown at March 3 encountered favorable environmental conditions resulting in significantly high economic yield compared to other sowing dates.

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