Between April 2006 and February 2008 plasma long chain fatty acids (LCFA) profiles were assessed every 8 weeks on individual blood samples from 27 Simmental cows, with lactation number from 1 to 6 selected from a dairy herd. Body condition score (BCS) and back fat thickness (BFT) were measured on the same day as the blood was taken. Assessment of the variability of plasma LCFA in relation to the influences of stage of lactation and season of the year was the main objective of this study. All of the fatty acids analysed presented differences (p<0.05) due to the stage of lactation as a factor. Plasma total LCFA amounts (mu g/ml) were higher in early lactation (1,641.4 +/- 513.85) in comparison with late lactation (1,473.67 +/- 336.05) and with dry Simmental cows (1,208.5 +/- 396.55). The sum of plasma MUFA (% of total fatty acids) was higher in the period of negative energy balance in early lactation (14.39 +/- 4.00) in comparison with mid (11.79 +/- 1.99) and late (11.93 +/- 2.14) lactation. Moreover, the sum of SFA was significantly higher in dry than lactating cows. Season had an impact on the sum of SFA (% of total fatty acids) which was higher in winter than summer, while the sum of omega-3 PUFA was higher in summer than winter. Also some individual plasma LCFA were significantly affected by the season and some individual plasma LCFA were affected by the interaction between stage of lactation and season of the year. In conclusion, the fatty acids profiles of Simmental cows were affected mainly by the stage of lactation and to a lesser extent by the season of the year.