Ocimum gratissimum essential oil (EOGT) has been evaluated for its antibacterial efficacy, and its combinational therapy with antibiotics may enhance the therapeutic efficiency against infection-causing bacteria. Herein, we evaluated the chemical composition of EOGT and its antibiotic efficacy against Staphylococcus aureus and Pseudomonas aeruginosa. GC-MS and GC-FID analyzed EOGT. The antibiotic efficacy was determined by the agar diffusion method, microdilution, minimum inhibitory concentration (MIC), and fractional inhibitory concentration index (FICI). Eugenol (74.2%) was the main component of OGT. Using the agar diffusion method, the action of rifampicin, ciprofloxacin, and tetracycline was evaluated against S. aureus, while the action of cefepime and ciprofloxacin was evaluated against P. aeruginosa. FICI showed a reduced MIC of ciprofloxacin and tetracycline associated with EOGT. In the presence of EOGT, MIC of ciprofloxacin reduced from 0.6 to 0.0006 μg/mL and of tetracycline decreased from 0.028 to 0.0018 μg/mL against S. aureus and from 4 to 0.12 μg/mL against P. aeruginosa. EOGT enhanced the antibacterial efficacy of the antibiotics suggesting a synergistic effect, thereby enhancing the efficacy in treating infection against S. aureus and P. aeruginosa.