Bartonella henselae is the causative agent of cat scratch disease (CSD) in human. Cat is considered the reservoir of the bacterium. Blood samples were collected between April-September 2005. From 100 domestic cats (indoor-outdoor) living in Tehran-Iran tested for Bartonella henselae bacteremia seroprevalence. Cultural and IFA method for serology were used. The IFA cutoff titer was >1:64. All blood samples from cats were cultured on fresh sheep blood agar for 4 weeks. For the comparison seroprevalence between groups, SPSS12 software and Pearson Chi-square were used with CI=95% and odd ratio determination. Bartonella was not isolated from these cats and no bacterial growth was seen. 23% (23 of 100) of cats had antibodies to B. henselae, detected by IFA at a titer >1:64.In our study there were no significant differences statistically in seroprevalence between cats and their owner. 18% of cat owners had antibodies to Bartonella henselae. Seroprevalence in control group (individuals which own no cat) was 5%, and in statistical comparison between cat owner and control group there were significant differences. Seroprevalence in cats more than 6 months and in outdoors cats were higher than the cats under 6 months and indoor cats. Our study confirm that indoor cats are less frequently infected than outdoor or stray cats and seroprevalence in cats as compare with their owner showed that contact with cats is a risk factor to infected with Bartonella henselae.