In this study, antibacterial activities of some essential oils against Paenibacillus larvae were investigated as an alternative to synthetic antibiotics used against American foulbrood (AFB), which causes serious damage to the beekeeping industry. Ten essential oils belonging to various species and carvacrol, the major component of Origanum onites oil, were analyzed. Besides examining the antibacterial activities of the essential oils in the experiments, composition of the oils was investigated by gas chromatography (GC) and GC-mass spectroscopy (GC-MS) analysis. The minimum inhibition concentrations (MICs) of the effective essential oils were also determined. The conclusions resulting from these observations were that Origanum onites oil showed the strongest antibacterial activity. Rosmarinus officinalis, Seseli andronakii, Pimpinella anisum, Heracleum platytaenium, Anethum graveolens, Bifora radians, and Seseli tortuosum were respectively found to be effective coming after Origanum onites. Seseli petraeum and Seseli resinosum, two different species within the same genus showed no antibacterial activity against AFB. The results show that composition of the essential oils is very important for antibacterial effect; in fact antibacterial effect is determined by the major component in the essential oil composition. However, intercomponent synergetic effect is as important as the major component itself according to the results of carvacrol experiments.