To determine the chemical composition and antimicrobial potential of marjoram (Origanum majorana L.) leaves extratcs obtained from Muğla, Turkey. The extract of ethanol, methanol, hexane, chloroform, isopropanol and water of marjoram were tested for antimicrobial activity against eleven bacterial strains and one yeast by disc diffusion method. The minimum inhibitory concentrations (MICs) of isopropanolic extract of marjoram leaves were determined using broth serial dilution method. The constitituents were analyzed by gas chromatography-mass spectrometry (GC/MS). The Shapiro-Wilk of Normal Distribution Test, Kruskal-Wallis and Mann-Whitney Tests were applied for statistical analysis in the study. All of the tested extracts, isopropanolic extracts of marjoram leaves showed the best inhibition zones against Klebsiella pneumoniae CCM 2318 (24 mm) and Candida albicans ATCC 10239 (28 mm), methanolic extracts against Staphylococcus aureus ATCC 6538/P (26 mm). In our study, the results of the inhibition zones are varied 6 to 26 mm against tested bacteria. The results of Mann-Whitney Tests showed that isopropanolic extract is a significant different from chloroform, water and hexane extracts, statistically (Pisopropanolic-chloroform=0.003, Pisopropanolic-water=0.000, Pisopropanolic-hexane=0.000). Isopropanolic extracts of O.marjorana were among the most active with the MIC values ranging from 0.008-64 mg/mL. MICs of O.marjorana L. different extracts obtained by the broth serial dilution method. The GC/MS analyses allowed fifteen compounds to be determined; the main constituents of the of isopropanolic extract of marjoram leaves was carvacrol %86.33. Carvacrol, major constituent of the marjoram isopropanolic leaf extract in our study, had possible antimicrobial activity by testing commercial carvacrol. It has been observed that the extracts can be used in the food industry to inhibit the growth of pathogens or as natural preservatives in foods.