Objectives: Many studies have investigated the utility of hepatitis B virus (HBV) serological markers in HBVinfected patients. However, only a few studies have examined HBV serological markers in HBV-human immunodeficiency virus (HIV) co-infected patients. Here, we conducted a cross-sectional study to evaluate correlations of HBV serological markers in treatment-naive HBV mono-infected patients and HBV-HIV co-infected patients. Methods: HBsAg, HBV DNA, HBV RNA, and HBcrAg were quantified in 51 HBV mono-infected patients and 33 HBV-HIV co-infected patients recruited at Tianjin Second People's Hospital from 2016 to 2019. Results: There was no significant difference in serum levels of HBV DNA (P = 0.056), HBV RNA (P = 0.387), HBcrAg (P = 0.714) and HBsAg (P = 0.165) between the patient groups. In HBV mono-infected patients, strong positive correlations were confirmed between HBV RNA and HBV DNA (r=0.620, P < 0.01), HBcrAg and HBV DNA (r=0.802, P < 0.001), and HBcrAg and HBV RNA (r=0.727, P < 0.01). In HBV-HIV co-infected patients, serum HBsAg was very strongly correlated with HBcrAg (r=0.838, P < 0.001). In HBeAg-positive HBV mono-infected patients, all HBV serological markers correlated with each other, whereas only HBV RNA correlated with HBcrAg in HBeAg-negative HBV mono-infected patients (r=0.688, P = 0.007). In HBeAg-positive HBV-HIV co-infected patients, only HBsAg correlated with HBcrAg (r=0.725, P < 0.001), whereas HBcrAg and HBV RNA correlated with each other in HBeAg-negative patients (r = 0.683, P=0.010). Moreover, CD4 T-cell counts were not significantly associated with HBsAg, HBV DNA, HBV RNA, and HBcrAg levels. Conclusion: Compared with HBsAg and HBV DNA, which are widely used in clinical settings, our study confirmed that new HBV serological markers, such as HBV RNA and HBcrAg, have some utility in HBV mono-infected patients and HBV-HIV co-infected patients for monitoring the progression of liver disease.