Q fever is a zoonosis caused by infection with Coxiella burnetii. Although the reservoir of C. burnetii consists of various species, the most common sources of human infection are farm animals, such as cattle, goats, and sheep. The agent is typically transmitted by the aerosol route, and in more than half of the cases primary infection is symptomless. Clinical outcomes of C. burnetii infection in domestic ruminants consist of abortion and stillbirths in sheep and goats, while in cattle it causes infertility and mastitis. A serological survey for C. burnetii was undertaken on a population of sheep. A total of 269 sheep serum samples were collected and tested for the detection of antibodies against C. burnetii phase I and II antigens using an enzyme-linked immunosorbent assay. The herd investigated was tested twice, i.e. in 2000 and 2009, to detect the changes in seroprevalence. In the first year of investigation, the prevalence of antibodies against C. burnetii phase II antigen was estimated at 37.22% and ten years later at 58.42%. Antibodies against phase I antigen were not detected in any examined serum samples. The difference in seroprevalence after ten years of observation was significant (p = 0.001).