Abstract: Objective:To explore the relationship between hepatitis B virus (HBV) infection and the pathogenesis of multiple my-eloma (MM), in order to provide an epidemiological evidence for the prevention and treatment of MM. Methods:Clinical and epidemi-ological data of 185 MM patients and 182 non-tumorous patients were collected. Subjects were randomly selected from in-patients who were homeochronously admitted to the same five grade- III A hospitals, including Xi'an Central Hospital, Shaanxi People's Hospital, Xi'an Jiaotong University Xibei Hospital, and so on. MM patients were selected in terms of age and gender. Peripheral blood HBsAg was assayed by ELISA. If HBsAg was negative, the S and C-gene fragments of HBV DNA were tested using nested PCR . Fisher's ex-act test or χ2 test (SPSS statistical software) was used to compare the differences between the groups. Logistic regression was employed to examine the association between the pathogenesis of MM and HBV infection. Results:In MM patients, the HBsAg positive rate was 8.11 % (15/185), the occult HBV infection (OBI) positive rate was 3.53% (6/170), and the total HBV infection rate was 11 .35% (21/185). For the control group, the HBsAg positive rate was 4.40% (8/182), the OBI positive rate was0.57%(1/174), and the total HBV in-fection rate was 4.95% (9/182). No statistical difference in HBsAg or OBI positive rate was found between the two groups ( P>0.05). However, MM patients showed significantly higher total HBV infection rate than that of the controls χ2=5.02, P<0.05; OR was 2.46 (95% CI:1.10- 5.53, P<0.05). Additionally, the proportion of ISS stage III was significantly higher in MM patients with HBV infection than in uninfected MM patients (85.71% vs . 60.37%,χ 2=5.15, P<0.05). Patients with HBV infection showed reduced albumin level (χ2=5.60, P<0.05) and a κ /λ light chain ratio (P<0.05) compared with uninfected patients. Conclusion:The risk of MM pathogenesis after HBV infection is significantly increased as OBI is included in the analyses. Furthermore, MM patients with HBV infection will develop more severe liver damage, indicating that OBI in MM patients with negative HBsAg should be screened before chemotherapy to prevent HBV reactivation.