Sponge are primitive multi-cellular organisms. They are important sources of secondary metabolites. In the previous studies indicated that the sponges harbor stable symbiotic microbial consortia. The mechanisms for maintenance and transmission of microbial consortia to the next generations are still not fully understood. The sponge, Cinachyrella australinesis, was chosen to further investigate relationship of the symbiotic bacteria within to the host. Fluorescent in situ hybridization ¡]FISH¡^was employed with non-specific ¡]EUB338¡^and specific oligonucleotide probes for bacteria. The sponge was cryo-sectioned¡]1£gm¡^and hybridized with fluorescent probes. The distribution and ratios of the bacteria in the sponge agreed with those of previous studies indicating that the symbiotic bacteria of C. australiensis are stable and endosymbiotic in nature.