The effects of season and cutting date on fatty acid composition of lipids from several alfalfa cultivars were significant, indicating the importance of the forage cutting date on the contribution of almost all fatty acids. In the present study, some slight differences in fatty acid composition of alfalfa lipids, according to the three different dormancy groups, were also found. It seems that an increase in the winter survivability, measured either by winter hardiness or autumn dormancy, has some basic impact on the fatty acids levels, even under non-freezing conditions (Alarcon Zuñiga, 2003). The proportions of 18:2n-6 and 18:3n-3 were higher in autumn compared with the other seasons, but the ratios 18:3n-3/18:2n-6 were higher in spring compared to summer and autumn. Cutting date also significantly affected in Experiment 2 the concentration of almost all fatty acids, total lipids and the ratios 18:3n-3/18:2n-6. The effects of cultivar or cutting date seem to be different because 18:1n-9 proportions were affected for cultivar and 18:0 proportions were only affected by cutting date. The results of Experiment 3 showed also some differences in the fatty acid composition due to the cutting date.