Aims Production and characterization of polyhydroxybutyrate (PHB) from moderately halophilic bacterium Vibrio harveyi MCCB 284 isolated from tunicate Phallusia nigra. Methods and Results Twenty-five bacterial isolates were obtained from tunicate samples and three among them exhibited an orange fluorescence in Nile red staining indicating the presence of PHB. One of the isolates, MCCB 284, which showed rapid growth and good polymer yield, was identified as V. harveyi. The optimum conditions of the isolate for the PHB production were pH 80, sodium chloride concentration 20 g l(-1), inoculum size 05% (v/v), glycerol 20 g l(-1) and 72 h of incubation at 30 degrees C. Cell dry weight (CDW) of 32 g l(-1), PHB content of 23 g l(-1) and final PHB yield of 12 g l(-1) were achieved. The extracted PHB was characterized by FTIR, NMR and DSC-TGA techniques. Conclusions An isolate of V. harveyi that could effectively utilize glycerol for growth and PHB accumulation was obtained from tunicate P. nigra. PHB produced was up to 72% based on CDW. Significance and Impact of the Study This is the first report of an isolate of V. harveyi which utilizes glycerol as the sole carbon source for PHB production with high biomass yield. This isolate could be of use as candidate species for commercial PHB production using glycerol as the feed stock or as source of genes for recombinant PHB production or for synthetic biology.