The cost-effectiveness of antiviral treatment in adult immune-tolerant (IT) phase chronic hepatitis B (CHB) patients is uncertain.We designed a Markov model to compare expected costs and quality-adjusted life-years (QALYs) of starting antiviral treatment at IT-phase ('treat-IT') vs delaying the therapy until active hepatitis phase ('untreat-IT') in CHB patients over a 20-year horizon. A cohort of 10 000 non-cirrhotic 35-year-old patients in IT-phase CHB (hepatitis B e antigen-positive, mean serum hepatitis B virus (HBV) DNA levels 7.6 log10 IU/mL, and normal alanine aminotransferase levels) was simulated. Input parameters were obtained from previous studies at Asan Medical Center, Korea. The incremental cost-effectiveness ratio (ICER) between the treat-IT and untreat-IT strategies was calculated.From a healthcare system perspective, the treat-IT strategy with entecavir or tenofovir had an ICER of US$16 516/QALY, with an annual hepatocellular carcinoma (HCC) incidence of 0.73% in the untreat-IT group. With the annual HCC risk ≥0.54%, the treat-IT strategy was cost-effective at a willingness-to-pay threshold of US$20 000/QALY. From a societal perspective considering productivity loss by premature death, the treat-IT strategy was extremely cost-effective, and was dominant (ICER <0) if the HCC risk was ≥0.43%, suggesting that the treat-IT strategy incurs less costs than the untreat-IT strategy. The most influential parameters on cost-effectiveness of the treat-IT strategy were those related with HCC risk (HBV DNA levels, platelet counts and age) and drug cost.Starting antiviral therapy in IT phase is cost-effective compared with delaying the treatment until the active hepatitis phase in CHB patients, especially with increasing HCC risk, decreasing drug costs and consideration of productivity loss.