Two octanordammaranes, mansumbinone (1) and 3,4-seco-mansumbinoic acid (2), and two sesquiterpenes, β-elemene (3) and T-cadinol (4) have been isolated from the oleo-resin of Commiphora molmol (Engl.). The structures of these compounds were established unambiguously by a series of 1D and 2D-NMR analyses. We have also unambiguously assigned all 1 H and 13C NMR resonances for 2 and revised its 13C data. The crude extract of the oleo-resin of C. molmol displayed potentiation of ciprofloxacin and tetracycline against S. aureus, several Salmonella enterica serovar Typhimurium strains and two K. pneumoniae strains. The antibacterial activity of terpenes 1–4 was determined against a number of Staphylococcus aureus strains: SA1199B, ATCC25923, XU212, RN4220 and EMRSA15 and minimum inhibitory concentration (MIC) values were found to be in the range of 4–256 μg/ml. The highest activity was observed by the seco-A-ring octanordammarane 2 with an MIC of 4 μg/ml against SA1199B, a multidrug-resistant strain which overexpresses the NorA efflux transporter, the major characterized antibiotic pump in this species. This activity compared favorably to the antibiotic norfloxacin with an MIC of 32 μg/ml. Compound 2 also displayed weak potentiation of ciprofloxacin and tetracycline activity against strains of Salmonella enterica serovar Typhimurium SL1344 and L10.