Background: Circulating microRNAs are endogenous, approximately 22 nucleotide non-coding RNAs that are overexpressed in many human cancers including hepatocellular carcinoma (HCC). Moreover, circulating miRNAs can reflect the level of serum miRNAs, so could be potential tumor markers. miRNA-21 regulates post-transcriptional expression gene which implies that miRNA-21 might be a novel diagnostic marker for cancer. Objective:ToevaluatethediagnosticpotentialofcirculatingmiRNA-21asatargetofmiRNA-21inHCCofEgyptianpatients. Patients and methods: This study was conducted on 35 patients had primary HCC without HCV, 35 patients infected with HCV and had primary HCC and 30 healthy subjects as a control. Serum alpha fetoprotein (AFP) was measured for all participants. The miRNA-21 was determined in whole blood samples using real-time PCR. The study was approved by ethics committee of Faculty of Medicine and National Liver Institute, Menoufia University, Egypt. Results: The results showed that the level serum AFP was a significantly elevated in both HCC (152.48 ± 126.90) and combined HCC + HCV (192.98 ± 132.55) groups when compared with its corresponding level in control group (3.37 ± 2.10) (p< 0.05. The data revealed up-regulation of micro-RNA 21 in both HCC (2.31 ± 0.69) and combined HCC+ HCV (4.99 ± 1.46) groups when compared with its corresponding level in control group (0.64 ± 0.94) (p< 0.05). Also, micro-RNA 21 expression was significantly increased in combined HCC + HCV group when compared with its level in HCC group (p< 0.05). Receiver Operator of Characteristics (ROC) curve analysis of plasma miRNA-21 revealed that, at a cut-off value in groups (2,3) > 2.0 and 2.3 while the sensitivity and specificity for differentiation of HCC cases were 91.43% and 94.29% and 86.67% and 90 %, respectively. while (ROC) curve analysis of AFP revealed that, at a cut-off value in groups (2,3) > 5.8and 6.4 while the sensitivity and specificity for differentiation of HCC cases were 86.57% and 74.29% and 80% and 93.33 %, respectively. Conclusion: Circulating microRNA-21 level could be used as a biological marker for HCC and it might be beneficial in early diagnosis. MicroRNA-21 and AFP could be used as co-biomarkers for HCC diagnosis.