[Objective] To investigate antimicrobial activity and metabolites of Streptomyces sp. from the termite nest. [Methods] Antimicrobial activities of fermentation broth against four pathogenic microbes were tested by Oxford cup method. The bioactive strain T12 was identified by molecular biology 16S rRNA sequence analysis. The active metabolites of T12 were isolated and purified from ethyl acetate crude extracts by various chromatographic methods, and their chemical structures were identified by mass spectrometry and nuclear magnetic resonance spectroscopy, and their antimicrobial activities were determined by filter paper method.[Results] T12 was identified as Streptomyces sp.. Under the concentration of 30 μg/filter paper, the ethyl acetate extract of T12 had potent antibacterial activities against Staphylococcus aureus and Candida albicans with inhibition zone diameters of 20.1 mm and 17.4 mm, respectively. Two metabolites including geldanamycin (1) and 17-O-demethylgeldanamycin (2), were isolated and characterized from fermentation broth. Both metabolites 1 and 2 exhibited good antimicrobial activity at the concentration of 30 μg/filter paper. The inhibition diameters of compounds 1 and 2 against S. aureus were 14.6 mm and 14.5 mm respectively, which were equivalent to those of gentamicin sulfate as positive control. The inhibition diameters of compounds 1 and 2 against C. albicans were 10.9 mm and 13.9 mm respectively, which were comparable to those of the referenced amphotericin. [Conclusion] Strain T12 could be potentially developed as a new microbial microbicide.