Background/Aims: The resistance of Helicobacter pylori to antimicrobials is an important factor compromising the efficacy of eradication therapy. It is known to be increasing in many countries. Therefore, the aim of this study was to evaluate antibiotic resistance rate of H. pylori for amoxicillin, clarithromycin, metronidazole and tetracyeline and to examine the mechanism of elarithromycin resistance in H. pylori strains isolated from Korean patients. Methods: One hundred eighty strains of H. pylori (95 strains in 2005, 85 strains in 2006) were isolated from 143 patients that had not received antibiotics, proton pump inhibitor, or nonsteroid anti-inflammatory drugs during preceding three months between 2005 and 2006 in Chung Ang University Yongsan Hospital. The distribution of minimum inhibitory concentrations (MICs) for the H. pylori isolates was examined by using the serial 2-fold dilution method. ATCC 43504 was used as standard strain. DNA sequences of 23S RNA gene in clarithromycin-resistant strains were determined by restriction fragment length polymorphism. Results: The resistant rates for amoxiciliin, clarithromycin, metronidazole and tetracycline were 7.2% (13/180), 8.9% (16/180), 36.1% (65/180) and 0% (0/180) between 2005 and 2006. The multi-drug resistance rate was 20.6%. Sequence analysis in clarithromycin-resistant strains showed A2144G mutations in 9 strains of 16 strains (56.3%) and T2183C mutations in 6 strains of 16 strains (37.5%). Sequence analysis in clarithromycin-resistant strains also showed one double mutation of both A2144G and T2183C in 1 strain of 16 strains (6.2%). The distribution of MICs in clarithromycin-resistant strains was relatively low from 2 to 16 μg/mL. Conclusions: The prevalence of clarithromycin resistance of H. pylori is relatively lower than previously reported in Korea. The PPI-based triple therapy including clarithromycin may be still effective eradication therapy of H. pylori in Korea. The A2144G mutation and T2183C mutation were mainly observed in clarithromycin-resistant isolates. Nation-wide surveillance of antibiotic resistance should be needed for further evaluation.