Feline infectious peritonitis virus (FIPV) is ubiquitous in domestic cats, especially in young cats and multi-cat environments. In the present study, a total of 248 companion cats of different ages were examined for serum antibody detection of FIPV by immunochromatography assay. The cats were selected from those referring to Veterinary Hospital of Ahvaz University, southwestern Iran from December 2006 to June 2009. Classification was made by age, sex, breed, region and season. The studied cats were divided based on age into three groups ( 3 years) and based on area into five regions (north, east, west, south and central). The results were analyzed by using Chi-square analysis and Fischer's exact test. Seventeen of 248 serum samples (6.85%) had antibody against feline infectious peritonitis virus. Prevalence was significantly higher in young kittens less than 6 months (9.72%; 7 out of 72) and mean-age cats 6 months – 3 years (9.28%; 9 out of 97) compared with above 3 years (1.27%; 1 out of 79) (P0.05). It is necessary to control cat population in these area particular young cats to reduce risk of infection transmission between them.