Aims Halophilic micro-organisms have received much interest because of their potential biotechnological applications, among which is the capability of some strains to synthesize polyhydroxyalkanoates (PHA). Halomonas sp. SK5, which was isolated from hypersaline microbial mats, accumulated intracellular granules of poly(3-hydroxybutyrate) [P(3HB)] in modified accumulation medium supplemented with 10% (w/v) salinity and 3% (w/v) glucose. Methods and Results A cell density of approximately 3.0 g l-1 was attained in this culture which yielded 48 wt% P(3HB). The bacterial strain was also capable of synthesizing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] when cofed with relevant precursors. Feeding with sodium valerate (0.7 mol l-1 carbon) at various time intervals within 36 h resulted in 3HV molar fractions ranging from 6 up to 54 mol%. Oil palm trunk sap (OPTS) and seawater as the carbon source and culture medium respectively facilitated a significant accumulation of P(3HB). Simplified downstream processing based on osmotic lysis in the presence of alkali/detergent for both dry and wet biomass resulted in approximately 90100% recovery of polymers with purity as high as 90%. Weight-average molecular weight (Mw) of the polymers recovered was in the range of 12 x 106. Conclusions Halomonas sp. SK5 was able to synthesize P(3HB) homopolymer as well as P(3HB-co-3HV) copolymer from various carbon sources. Significance and Impact of the Study This is the first time a comprehensive study of both production and downstream processing is reported for Halomonas spp.