[Background] Marine microorganisms have a great application potential in developing bioactive substances, but few researches reported so far on microorganisms in the east island of the south China sea. [Methods] Marine culturable bacteria isolated and purified from sediments from Donghai island were identified by morphological observation, physiological and biochemical analysis, and phylogenetic analysis of 16S rRNA gene sequence. Escherichia coli, Bacillus subtilis and Staphylococcus aureus were used as indicators to determine their antibacterial activities. Based on the study on bacteriostasis of sediment bacteria, Polyketide synthase I (PKSI) gene was screened for strains with bacteriostasis activity, and amino acid sequence alignment of PKSI positive bacteria was performed. PKSI positive representative strain was selected to test the stability of the strain and its fermentation bacteriostasis. [Results] In total 25 bacteria were isolated and purified, belonging to 9 genera: Acinetobacter, Alteromonas, Bacillus, Psychrobacter, Pseudoalteromonas, Oceanimonas, Staphylococcus, Micrococcus and Marinobacter. Through the screening of bacteriostatic activity and PKSI gene, 6 strains had bacteriostatic activity, and their bacteriostatic substances all contained ketone compounds. It was speculated that DHD-15 and DHD-a might contain novel structure of type I polyketide synthase. DHD-15 and DHD-L can grow normally between 15 and 40 ℃, and grow best at 1% salt concentration and pH between 4 and 6 in seawater. [Conclusion] There are relatively rich culture-able bacterial resources in the sediments of Donghai island, south China sea.