The objective of this study is to analyze factors affecting Hepatitis B Virus (HBV) reactivation in anti-HBc positive patients with Non-Hodgkin's lymphoma treated with rituximab and compare HBV reactivation rates by duration of prophylactic treatment with tenofovir to contribute to the establishment of an effective prevention strategy.

This study will be conducted in a randomized, open-label, multi-center design. On Day 1 of chemotherapy, approximately 90 subjects screened and determined eligible will be randomized to either Group A or Group B in a 1:1 manner for study participation.

• Group A: Upon the EOC, subjects will receive tenofovir 300mg for approximately 6 months (24 weeks) and undergo treatment and follow-up every 12 weeks for up to 72 weeks post chemotherapy.
• Group A: Upon the EOC, subjects will receive tenofovir 300mg for approximately 12 months (48 weeks) and undergo treatment and follow-up every 12 weeks for up to 72 weeks post chemotherapy.

Inclusion Criteria:

1. Age of ≥ 18 (Women must not be pregnant or breast-feeding; all females of childbearing potential must have a blood test or urine study during screening to rule out pregnancy. / A woman of childbearing potential must be using an adequate method of contraception to avoid pregnancy throughout the study and for up to 26 weeks after the last dose of tenofovir. / If the Investigator obtains information concerning the pregnancy of a female patient, the Investigator must terminate the study drug immediately in that patient, and report the information to IRB in the same manner as for SAE reporting)
2. CD 20 positive patients with Non-Hodgkin's lymphoma who are planned to receive anticancer treatment with rituximab based chemotherapy and A. ECOG performance status 0-2 B. Adequate renal function: serum creatinine level < 2 mg/dL (177 μmol/L) C. Adequate hematological function: hemoglobin ≥ 9g/dL, absolute neutrophil count (ANC) ≥ 1,500/μL, platelet count ≥ 75,000/μL, unless abnormalities are due to bone marrow involvement by lymphoma D. Expected residual life ≥ 6 months
3. Serum HBsAg negative, anti-HCV negative, but anti-HBc positive
4. ALT < 80IU/mL, serum bilirubin < 3.0mg/dL, unless abnormalities are due to liver involvement by lymphoma or tumor lysis syndrome
5. Individuals who were given and understood detailed explanations about this study, voluntarily decided to participate in the study, and provided written informed consent

Exclusion Criteria:

1. Child-Pugh class C
2. Other chronic liver diseases such as autoimmune hepatitis or Wilson's disease
3. Patient who has hypersensitivity to study drug
4. Patient who has galactose intolerance, Lapp lactase deficiency, glucose-galactose malabsorption
5. Patient who is pregnant or on lactating. Or who has plans for pregnant or lactation during study period even the partner of the male patient