In this study, the in vitroinfluence of antibacterial activity of amoxicillin and tetracycline on each other was investigated by macrobroth dilution and checkerboard assay methods. Each of the antibiotics as well as their combinations proved inhibitory against all the tested organisms with the exception of Acinetobacter calcoaceticus showing high level of resistance. The inhibition zones produced by the combination of tetracycline and amoxicillin with those obtained from each antibiotic showed synergistic interaction which is concentration dependent. The checkerboard assay results showed 87.5 synergy and 12.5% antagonism with a high reduction in the Minimum Inhibitory Concentrations (MICs) and a strong bactericidal activity against the test organisms. Results of macrobroth dilution and checkerboard assays are complementary and indicated a strong synergistic interaction between amoxicillin and tetracycline.