en Virology Virology Original Research Original Research <strong>Background: </strong>The microRNA‐122 (miR‐122) is a liver‐specific microRNA that can be used as a potential molecular marker for predicting liver injury. There is a positive correlation between miR‐122 level in serum and hepatitis B virus (HBV) replication in patients infected with this virus. The present study was conducted to study the clinical importance and expression of miR-122 in asymptomatic and symptomatic patients with HBV infection in comparison to the healthy group.<br> &nbsp;&nbsp; <strong>Methods:</strong> This study was performed on 60 samples to examine the presence of HBsAg and total HBc antibody (IgM-IgG) using an enzyme-linked immunosorbent assay. HBV-DNA extraction and real time polymerase chain reaction (PCR) assay were performed on all samples via the Real ART HBV LC PCR kit on a LightCycler instrument. RNA was extracted from the serum of all participants. Next, miRNA expression was assessed using quantitative real time reverse-transcription PCR. Also, ALT levels were measured as a surrogate parameter for liver injury using Pars Azmoon Biochemical assay Kit on Hitachi autoanalyzer. The Levene , Kruskal Wallis, Mann-Whitney and Spearman&rsquo;s correlation tests were used for assessing the differences between the studied groups.<br> <strong>&nbsp;&nbsp; Results:&nbsp; </strong>Based on the obtained results, miR-122 expression in patients with HBV without clinical symptoms was 1.6 times, while in patients with clinical symptoms was 2.7 times more than the control group (p=0.001). A significant increase was observed in the ALT enzyme of symptomatic patients (p=0.001). HBV DNA in the people with clinical symptoms was higher than 105 copies/mL and in the asymptomatic group was less than 103 copies/mL, suggesting a statistically significant increase in a group with clinical symptoms (p=0.001). Finally, it was found that the miR‐122 serum concentration correlated with HBV DNA and serum ALT (p=0.001).<br> &nbsp;&nbsp; <strong>Conclusion:</strong> Based on the obtained results, measuring the miR-122 levels can serve as a biomarker and an indicator of hepatitis B replication, especially in cases where ALT levels are unchanged; however, more research and more samples are needed.<br> &nbsp; MicroRNA, Hepatitis B, MiR-122, ALT 1028 1031 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1473-3&slc_lang=en&sid=1 Rana Tabar Asad Laleh z.sharifi@ibto.ir 200319475328460065934 200319475328460065934 No Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, Tehran, Iran Zohreh Sharifi z.sharifi@tmi.ac.ir 200319475328460065935 200319475328460065935 Yes Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, Tehran, Iran Ali Akbar Pourfathollah z.sharifi@ibto.ir 200319475328460065936 200319475328460065936 No Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, & Departments of Immunology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran