Context Essential oils (EO) are known to inhibit the growth of bacteria responsible for mastitis in dairy cows. We recently have found that, among 10 medicinal promising Mediterranean plants, Thymus capitatus essential oils (TCEO) has the highest anti-microbial effects against Staphylococcus aureus strains isolated from mastitis dairy cows. Aims. The aim was to test whether the antibacterial effects of TCEO were accompanied by any anti-inflammatory activity in in vivo and in vitro models, by measuring gene expression and cytokine secretion of the major inflammatory components, and by studying the evolution of somatic cell counts (SCC) in milk for the in vivo model. Methods. In vivo study: 12 Holstein cows with subclinical mastitis were assigned to either control (n =6) or EO (n = 6) group. Udder infected in the EO group was treated two times daily, after the milking, with TCEO diluted in milking grease for 7 days. Milk samples were collected to measure the level of IL8, SCC and for bacteriological analysis. We measured the abundance of some inflammatory genes on PBMC isolated cells. Statistical analysis was carried out by using one-way ANOVA. In vitro study. PBMC were purified from fresh blood derived from 3 healthy cows stimulated with LPSand with TCEO or its major components. The secretion of inflammatory cytokines in the culture supernatant was measured by using a Bovine Cytokine/Chemokine Magnetic Bead Panel. Results. No statistical differences on SCC, IL8 secretion in the milk, bacteriological status, nor PBMC cytokine gene expression were observed between Control and TCEO groups in the In vivo model. These preliminary results suggest that the antibacterial effects of TCEO highlighted in the In vitro study were not followed by any anti-inflammatory in vivo effects against mastitis. Further analyses are in progress to evaluate the anti-inflammatory activity of TCEO and its major components in the In-vitro model.