West Nile fever is an emergent zoonosis caused by an RNA virus of the family Flaviviridae of the genus Flavivirus. Virus naturally circulates between birds, which are reservoir hosts and mosquitoes, primary genus Culex, which are vectors. Except in birds and poultry, infection is also confirmed in many mammals. Along with the birds, in which majority of species don't show clinical symptoms at all, while for some mortality rate is high, clinical manifestation is most common in horses and people. People are almost exclusively infected during the feeding of infected mosquitoes, which is also the primary route of transmission of infection in animals. So, to show the evidence of virus circulation in a particular area, for the purpose of anti-epidemic measures, sentinels survaillance programs are being implemented in order to confirme the presence of infected mosquitoes by detecting infected sentinel animals in certain areas. Horses and poultry are most often used domestic animal species for this purpose. This generally effective system has limitation in its implementation in urban areas. Therefore, the aim of this study was to investigate West Nile virus infection in dogs and cats and by achieving that, also to investigate the possibility of using them as sentinels in urban areas. For this purpose, a total of 184 dog and 92 cat sera samples were tested using a commercial ELISA test (INgezim West Nile Compac) for the determination of IgG antibodies for the West Nile virus. All tested animals were from the Grad Zagreb and Zagrebačka county area. Seroprevalence established in dogs was 5,98%, while in cats 4,34%. There was no significant difference between seroprevalences in these species nor the influence of the breed, sex, or clinical symptoms on seroprevalence. The first evidence of infection in both species was confirmed in September, and all animals younger than 4 years were negative. Results of this study confirm the West Nile virus infection in dogs and cats for the first time in Croatia. With the analysis of the achieved results, it is confirmed that dogs and cats can be sentinels in urban areas. By using dogs and cats as sentinels a relevant data for surveillance and control of this zoonosis can be collected. Hence, ongoing West Nile virus surveillance programs should be upgraded with testing dogs and cats in urban area to improve surveillance of this important arboviral zoonosis in accordance with the „One Health“ approach.