• Male ≥18 years and ≤75years of age;

• Confirmed diagnosis of hemophilia B (baseline FIX activity ≤ 2% of normal or documented history of FIX activity ≤2%);

• At least 100 days exposure history to FIX;

• Currently receiving FIX Prophylaxis therapy or on-demand treatment to prevent bleeding;

• Have acceptable laboratory values:

‣ Hemoglobin ≥110 g/L;

⁃ Platelets ≥100×10'9 cells/L;

⁃ AST, ALT, alkaline phosphatase ≤2×upper limit of normal (ULN) at the testing laboratory;

⁃ Bilirubin ≤3× ULN ;

⁃ Creatinine ≤1.5× ULN.

• No measurable factor IX inhibitor as assessed by the central laboratory and have no prior history of inhibitors to factor IX protein;

• Agree to use reliable barrier contraception until 3 consecutive samples are negative for vector sequences;

• Able to provide informed consent and comply with the requirements of the study.