A new bioactive oxygenated homoditerpenic compound along with one known compound from the antimicrobial active ethanol extract of leaves of an endemic plant Centaurothamnus maximus was isolated. The n -hexane, dichloromethane, ethyl acetate and ethanol fractions of C. maximus leaves were evaluated for their antimicrobial potential by using standard agar well diffusion method against various microorganisms viz. B. subtilis, S. aureus, E. coli, P. aeruginosa, C. albicans and M. smegmatis. The results revealed that only ethanol extract was active against all microbes except the fungus C. albicans. A new compound 2α, 3α-dihydroxy-8α-methoxy-15-hydroxy-methylene- pimar-5,9 (11)-diene (CM-1) was isolated along with a known compound α-D-xylose (CM-2) from ethanol extract by reverse phase (RP-18) column chromatography and 1D and 2D NMR (DEPT, COSY, HMBC and HSQC) aided by EIMS mass and IR spectra were used to establish the structure. CM-1 was found to be active against B. subtilis, S. aureus and M. smegmatis (P>0.005) at MIC 20 μg/ml. Findings of this study may provide a lead for synthesis of more potent antimicrobial agents to serve the humanity against multidrug-resistant bacterial infections.