It has been demonstrated that liver microRNA-125a-5p (miR-125a-5p) is correlated with disease progression in different liver diseases, including liver fibrosis and hepatocellular carcinoma (HCC). The present study investigated whether serum miR-125a-5p correlated with the progression of different liver diseases. Serum samples were obtained from healthy individuals, patients with chronic hepatitis B who had undergone a liver biopsy, and patients with HCC and were analyzed for the levels of miR-125a-5p. Compared with the healthy controls, the serum levels of miR-125a-5p were significantly higher in the liver fibrosis serum, and were reduced in HCC. With the development of liver fibrosis, there was a significant increase in the expression of miR-125a-5p (P<0.05). In comparing histological activity index (HAI) scores, higher expression levels of miR125a-5p were observed in the high HAI score group (P<0.05). Furthermore, correlation between serum miR-125a-5p and viral replication (P<0.001) was observed. Notably, miR-125a-5p demonstrated significant correlation with other markers in the liver fibrosis group (P<0.001). In the patients with HCC, lower serum levels of miR-125a-5p were correlated with a poor prognosis, determined by Kaplan-Meier curve analysis (P=0.009). In the liver fibrosis and HCC groups, different expression levels of serum miR-125a-5p were observed, and were correlated with disease progression. The results of the present study suggested that serum miR-125a-5p may be used as a non-invasive biomarker for monitoring disease progression in liver diseases.