A total of 106 actinomycetes were isolated from Thai mangrove sediments using Gauze No.2, M4, Raffinose-histidine plus gellan gum, Waksman and water proline as selective media. Screening of antimicrobial activity revealed an interesting result of anti-Micrococcus luteus (60.9%), anti-Methicillin-resistant Staphylococcus aureus  (52.1%), anti-Staphylococcus aureus (46.7%) anti-Pseudomonas fluorescences (41.3%), anti-Candida albicans (39.1%), anti-Aeromonas hydrophila (26.1%), anti-Vibrio parahaemolyticus (7.6%) and anti-E. coli 0157 (1.1%), respectively. Genus Streptomyces was mainly found. Four of the potent anti-microbial isolates, AV2-6-4, AV2-5-14, AV2-1-9 and Rh1-5-10, were selected to culture in ISP2 medium and extract for crude products.  The results from bioautography assay showed that all crude extract have at least 4 active components.The molecular identification by 16S rRNA gene sequencing analysis revealed that AV2-6-4 was 99.44 % similar to Streptomyces violaceusniger NBRC 13459, S. yogyakartensis NBRC 100779 and   S. javensis. NBRC 100777, AV2-5-14 was 98.93% similar to Streptomyces iranensis HM 35 and S. yatensis NBRC 101000, AV 2-1-9 was 99.70 % similar to S. misionensis NBRC13063 and Rh 1-5-10 was 99.44 %  similar to S. albiflaviniger NRRL B-1356, respectively.