Abstract: Objective To analyze the correlation between hepatitis B virus (HBV) genotypes and drug-resistance mutations with HBV reactivation (HBVr) in tumor patients, and to provide evidence for antiviral treatment and prevention of HBVr in clinical oncology practice. Methods Methods A total of 130 serum samples positive for HBV-DNA were collected from hospitalized tumor patients between January 2019 and December 2022, including 26 cases in the HBVr group and 104 cases in the non-HBVr group. HBV genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The reverse transcriptase (RT) region of the polymerase gene was amplified by nested PCR, and Sanger sequencing was conducted to identify resistance-associated mutations and drug-resistance profiles. The sequencing results were analyzed using MEGA 11.0 software to compare RT region sequences. Statistical analyses were performed using SPSS 19.0 software. Results Among the 130 tumor patients with HBV infection, 16 cases were genotype B, 100 were genotype C, and 14 were mixed B+C, with genotype C as the predominant type (P<0.001). Drug-resistance mutations in the RT region were detected in 34 cases (26.15%), involving 13 types of resistance mutations and 3 mutation patterns, mainly in genotype C. The major mutations were as follows: for ADV, rtN236T, rtV214E/A, and S219A+L217R; for LAM, rtL180M+M204I/V and A181S+T184 ; for ETV, S219A+L217R and rtL180M+M204V +S202G/I ; and for LdT, rtL180M+M204I. Mutations associated with corresponding HBsAg variations included A181V, M204V , M204I, and rtS202I, with M204I causing two amino acid (Aa) changes in HBsAg: sW196L or sW196* (stop codon). There was no significant difference in HBV genotype distribution between the HBVr and non-HBVr groups (P>0.05), but significant differences were found in RT region drug-resistance mutation patterns and overall drug-resistance rates between the two groups (P<0.05). No significant difference in genotype distribution was observed between hepatocellular carcinoma and other tumor patients (P>0.05), nor in the distribution of HBVr and non-HBVr subgroups within these populations (P>0.05). Conclusions HBV genotype is not significantly associated with HBVr, whereas drug-resistance mutations in the RT region show a significant correlation with HBVr. It is recommended that HBV-infected tumor patients undergo monitoring for RT region drug-resistance mutations or receive antiviral therapy using nucleos(t)ide analogs (NAs) with a high genetic barrier to resistance to prevent HBVr.