The objective of the investigations performed was to study the influence of marine fish oil added to the feed for moulted hens on the content of fatty acids in the yolk of their eggs, in particular on the longchain polyunsaturated fatty acids in an ‘n-3’ family (n-3 PUFA). The experiments were conducted using ISA Brown hens (86-98 weeks of age – the second productive period) divided into two groups (32 hens in each group): a control group (group I) fed on the DJ basic diet with 1,5% soybean oil and an experimental group (group II) fed on the DJ diet containing 1,5% of marine fish oil (MFO). From each group, 30 eggs were taken three times; their fatty acid contents were measured and analysed each time. The statistically significant differences were found in the majority of fatty acids. And interesting results were stated in the content levels of polyunsaturated fatty acids. In the egg yolks of the experimental group, there was a significant and favourable decrease of about 55% in the n-6 PUFA: γ-linolenoic (C_18:3), arachidonic (C_20:4), docosatetraenoic (C_22:4), and docosapentaenoic (C_22:5)- A significant increase (averagely of about 60%) in the n-3 PUFA was stated: EPA, DPA and DHA, if compared with a control group. The ratio: n-6 to n-3 essentially decreased from 6.35 in the group I to 5.16 in the group II.