Background and objectives: Due to the unparalleled availability of their chemical diversity, natural products from either pure compounds or standardized extracts offer limitless opportunities for drug discoveries. This study focused on developing potent antimicrobial agents derived from Streptomyces strains isolated from mangrove ecosystems, which are known to produce antibacterial secondary metabolites. Materials and methods: A total of 28 cultures of actinomycetes were isolated from mangrove soil samples of Hainan province, China. The isolates were identified and tested for their antibacterial activities against different pathogenic bacteria. The active metabolites of all isolates were extracted and assessed for antibacterials and antibiofilm activities. Results: Four isolates designed as NELs-10, NELs-20, NELs-30 and NELs-40 were selected for having strong antibacterial activities against different pathogenic organisms and identified as Streptomyces sp. The supernatants suggested that extracellular active substances of these strains that significantly reduce the biofilm formation of the pathogenic bacteria. All the crude extracts displayed strong activities against the test organisms with the MIC were ranged from 15.62 to 1000 µg/mL. Most of the antimicrobial substances exhibited strong activities, heat stability between 40 ºC and 100 ºC and were active in a broad pH range from 2.0 to 12.0. Conclusion: The present study confirms that the crude extracts contain antibacterial compounds, which could serve as promising agents for controlling bacterial infections.