Aims: The aim of this study was to assess the distribution of GBS-related lipo-oligosaccharide (LOS) classes and capsular genotypes among Iranian clinical C. jejuni strains and to assess its relation with dnaK gene expression. Moreover, a comprehensive study of C. jejuni MLST-genotypes and global comparison with peer sequences worldwide was intended.Methods: Distribution of sialylated-LOS classes and specific capsular genotypes were investigated in C.jejuni of clinical origin. The expression of dnaK in C. jejuni strains was measured by Real-Time-PCR. MLST-genotyping was performed to investigate the clonal relationship of clinical C. jejuni strains and comparison with global sequences worldwide.Results: C. jejuni HS23/36c was the predominant genotype (45%), followed by HS2 (20%), and HS19 and HS4 (each 10%). A total of 80% of isolates were assigned to LOS class B and C. Higher expression level of dnaK gene was detected in strains with HS23/36c, HS2 and HS4 capsular genotypes and sialylated LOS classes B or C in this study. MLST analysis showed that isolates were highly diverse and represented 6 different sequence types and 3 clonal complexes. ST-21 and ST-257 complexes were dominants (75%) in our C.jejuni strains. The CC21 was the largest CC in our collection which is consistent with global C.jejuni strains worldwide. No new ST and no common ST with our neighbor countries was detected in this study.Conclusion: Global analysis of MLST results demonstrated that ST-50 (CC21) was widely distributed in different countries, while ST-19 (CC21) and ST-257 (CC257) was less ubiquitously spread. Overall, CC21 and CC353 complexes were most frequent and most widely distributed clonal complexes around the world; although, CC353 was not detected in this study. This shows a picture of movement of dominant Campylobacter strains worldwide. The occurrence of identical clonal complexes with different capsular types and LOS classes in this study is consistent with genetic variation in circulating identical genotypes and their evolution toward different pathotypes probably through acquisition of different genetic elements including LOS and CPS gene clusters.