The experiment was carried out with dual-purpose fowls developed for rural backyard farming – indigenous Katunitsa chicken (line “AN”), in a free range management system from hatching to 52 weeks of age. The purpose of the investigation was to establish the influence of a blend of herbs as a dietary supplement on some serum biochemical parameters (alanine aminotransferase, aspartate aminotransferase, total cholesterol, gamma-glutamyl transferase, triglycerides and creatinine), growth performance, egg production, egg fatty acid composition, and health status. The composition of this blend of herbs included: 0.05% garlic powder (Allium sativum), 0.3% cinnamon powder (Cinnamomum verum) and 0.03% of each of the following dried herbs: yarrow (Achillea millefolium), rosemary (Rosmarinus officinalis), thyme (Thymus serpyllum), basil (Ocimum basilicum) and oregano (Origanum vulgare). The birds were divided into two groups – control (n=60) without supplemental mixture to the diet and experimental (n=700) with supplemental mixture to the diet from the first day of age to the end of the experiment. The results showed that the herbal mixture supplement decreased significantly the blood serum cholesterol and triglyceride levels – at 7 (P<0.001) and at 52 weeks (P<0.05) of age. The content of phospholipids, triglycerides and linoleic acid in the egg yolk was higher in the experimental group compared to the control group (Đ<0.05). There was no significant difference in the egg yolk cholesterol levels between both groups (P>0.05). Over the entire investigation period the chickens from the experimental group had a better feed conversion ratio (with 3.37%) and a higher egg laying capacity (with 1.79%). At the end of experiment (52 weeks of age), hens from the control group exhibited generalised fatty degeneration of liver parenchyma, while these in experimental group, the major part of hepatocytes had no fat droplets in their cytoplasm. The death rate from 0 to 7, from 8 to 21 and from 22 to 52 weeks of age was 18.33%, 0% and 8.57% in the control group and 1.00%, 0.26% and 2.62% in the experimental group, respectively. Therefore in conclusion, it can be affirmed that the use of this blend of herbs had a beneficial effect in the treated fowls and improved their egg productivity, vitality and health condition.