Milk fat is from a nutritional point of view of the negative evaluation because of the dominant content of saturated fatty acid with high atherogenic index. Intake of milk fat in the diet is important because of the content of monounsaturated fatty acids, acting favorably against cardiovascular diseases and especially of essential fatty acids, linoleic, alpha linolenic and conjugated linoleic acid (CLA), which is found only in meat and milk of ruminants. These are precursors of biologically active substances - hormones and enzymes. The analysis of relations of fatty acids in milk fat to qualitative-production parameters of milk shows that the correlations of fatty acids with lactation stage and qualitative-production parameters of milk are quite weak in dairy cows with stable type of nutrition in form of whole-the-year feeding mixed feed ration in lowland agricultural area. Changes in milk fat composition are caused by the change in the ratio of de novo and depot fatty acids. Relation of fatty acids to the evaluated parameters lies with their metabolic origin and neither acid nor group underlies the specific influence of the studied parameters, by the means of which it would be possible to influence its proportion in milk fat. And so it is not possible to influence some group or a desirable fatty acid, e.g. CLA, without the influence on total milk fat.