Regarding to Q fever which is one of the most important zoonoses in Food (Milk) Hygiene and in Environmental Public Health, a sero-epidemiological study was carried out to detect the complement fixation antibodies to Coxiella burnetii Nine Mile strain phase II antigen among the milking cows in Kyunggi Province. The results obtained were summarized as follows: 1. The overall prevalence of the CF antibodies to Q fever among 989 milking cows of 75 dairy farms in Kyunggi Province was revealed as high as 58.7% by the farms and 27.8% by the individual cows with higher prevalence in Kyunggi Central and Kyunggi East regions than any other regions in the Province. 2. Anticomplementary reactions were appeared as 7.5% (74/989) and it ranged from 1.0% to 16.0% according to the regions investigated. 3. In the titration of the positively reacted sera, the figures of 16.7%, 37.5%, 29.8%, 9.5%, 2.9% and 3.6% at the serum dilutions of 1: 10, 1: 20, 1: 40, 1: 80, 1: 160 and higher than 1: 160, respectively. 4. It was recognized that the relatively higher cumulated frequency distribution of the CF antibodies was shown in the sera collected from the regions with higher prevalence of Q fever. 5. There was a high correlation between the prevalence of Q fever CF antibodies and the age which is usually equivalent to one year older than the calving history of the milking cows.