The elimination of HBsAg is the final goal of hepatitis B treatment, but is ra'rely achieved. The aim of the study was to assess on treatment serum HBsAg kinetics to predict 5upression of HBV DNA in patient with chronic hepatitis B treated TDF. The study included 60 patients with CHB. They were given TDF 300mg/day and serum samples were obtained in weeks 0, 12, 24. HBV DNA was measured by realtime PCR. Quantitative HbsAg was studied by Roche elecsys HbsAg II quant. TDF treatment progressively reduced serum HBsAg levels from baseline 4.79 log1oUl/ml, at week 12 - 4.37 log10Ul/ml, at week 24 - 4.13 log10Ul/ml. During 6 months, patterns of HBsAg decline were observed rapid 1 log10Ul/ml in 13/60patients, slow 1 log10Ul/mi in 42/60 patients, steady in 5160 patients. No difference in serum HbsAg levels between biological response, seroconversion and non biological response seroconversion HBeAg. During treatement, serum HBsAg levels decreased only in patietnts who developed rapid suspression of HBV DNA at week 12 (3.74 log10Ul/ml), week 24 (3.61 log10Ul/ml). In conclusion, quantitative serum HBsAg is a new marker in the prediction of virus responses in treatment of chronic hepatitis B.