It has been reported that all major chlamydial species can inhibit host cell apoptosis and the Chlamydia trachomatis antiapoptotic activity is correlated with inhibition of activation of the proapoptotic multidomain Bcl-2 proteins Bax and Bak and degradation of BH3-only domain Bcl-2 proteins such as Puma. The current study is to test whether the more invasive species can also suppress host apoptosis through inhibition of Bax and Bak activation. We compared the effects of the three invasive chlamydial species C. muridarum, C. caviae, C. psittaci with that of C. trachomatis on host cell Bax and Bak activation. We found that these chlamydial species not only failed to activate Bax and Bak but also significantly inhibited Bax and Bak activation, mitochondrial cytochrome c release and caspase 3 activation induced by staurosporine. These results have demonstrated that inhibition of host cell apoptosis pathways mediated by Bax and Bak activation is a common property of the major chlamydial species.