In total, 796 serum samples of sheep on commune alpine pastures in the region of Vorarlberg were investigated by a commercial ELISA kit for antibodies against Chlamydia abortus, the agent of ovine enzootic abortion. The aim of the study was to determine the seroprevalence within this region and to compare these results with the seroprevalence in the neighboring canton Graubünden as well as to obtain data on the seroconversion after alpine pasturing. Therefore, 421 samples were collected before and 375 samples after alpine pasturing, whereas corresponding serum samples were available from 359 sheep. Within the region of Vorarlberg, a mean seroprevalence of 9.2 % was calculated with a threshold of 60 %. Seroconversion for C. abortus occurred in 5.0 % of animals with corresponding serum samples. Seroprevalence values were comparable to Swiss regions with similar management systems, although the neighboring canton Graubünden is known to have a much more higher seroprevalence of 43 %. In conclusion, the traditional animal exchange between these two regions is not significantly favoring the spread of C. abortus.