Recently, polyhydroxyalkanoates (PHA) have garnered systematic attention as biodegradable alternatives to petrochemical plastics. This study aimed to identify bacterial strains synthesizing poly(3-hydroxybutyrate) (PHB) from Vietnam's coastal zones. Strain BTNC26, isolated as a PHA producer, was identified as Salinicola lusitanus BTNC26 via 16S rRNA gene sequencing (GenBank: PZ087081). Optimization of carbon (glucose) and nitrogen (yeast extract) sources, pH (7), temperature (30°C), and NaCl (5%) enhanced cell growth and PHA accumulation. Under these conditions, biopolymer yield reached 73.07% after 3 days. FTIR, GC–MS, and NMR confirmed PHB identity: FTIR showed a carbonyl peak at 1710.52 cm⁻¹; ¹H/¹³C NMR revealed resonances at 169.14 (C = O), 67.62 (–CH–), 40.80 (–CH₂–), and 19.76 ppm (–CH₃); GC–MS displayed the 3-hydroxybutyric acid methyl ester molecular ion. Scale-up fermentation (200 mL to 100 L) with 10 g/L glucose supplementation yielded PHB concentrations of 4.76, 4.23, 3.98, and 3.59 g/L at 200 mL, 1 L, 10 L, and 20 L, respectively. Composite films incorporating extracted PHB with PBAT, CaCO₃, PEG, and glycerol exhibited thin, strong, and flexible properties, with biodegradability confirmed in laboratory seawater assays. These findings highlight the potential of halophilic S. lusitanus for seawater-degradable PHB production, informing strain- and condition-specific strategies for industrial scalability.