The essential oils of Thymus persicus and Thymus eriocalyx were collected in Lorestan province, west of Iran and were examined by GC/MS and bacteriological tests. Twenty seven compounds representing 92.095% of T. persicus and 99.77% of Thymus eriocalyx essential oils were identified. The major constituents of T. persicus were thymol (10.71%), carvacrol (25.71%), gamma-terpinene (5.63%), alpha-pinene (1.14%), beta-pinene (1.02%), limonene (11.65%) trans-sabinene hydrate (7.78%) and 1-borneol (4.07%) and the major compounds of T. eriocalyx. were 1, 8-cinole (3.07%), L-linalool (1.01%), thymol (66.34%), caryophyllene oxide (2.96%) and carvacrol (7.5%). The oils also were examined for antibacterial activities against 6 standard bacteria by the broth microdilution and disc diffusion methods. They exhibited significant antibacterial activities against Staphylococcus aureus (MIC =1 : 235, MBC =1:20), Escherichia coli (MIC = 1:320, MBC =1:80) and Pseudomonas aeroginosa (MIC = MBC = 1:1280). The results were compared with control antibiotics.