Objective: To evaluate efficacy of vaccination against tick-born encephalitis by determination of specific antibody titer. Materials and Methods. 224 vaccinated residents (77 females, 147 males) of Selenge aimag with mean age of 33.1(6- 60), 20 worker of Ulaanbaatar with mean age of 36 (23-53) were enrolled to the study. We used Avidity determination of antibodies againt TBE Virus ELISA (Ig G) manufactured by the EUROIMMUN.Result:At 2-6 months after first dose RAI% was in low (29.4-32%), at 1 month after second dose RAI% was in equivocal (53.9%-55.6%), at 6 months after third vaccination RAI% was in high (72.5%-79.8%) avidity antibodies in two groups. That mean RAI% is increasing depend from repetition doses in both schedule. These differences were statistically significant for all post vaccination evaluation days (60,90; p<0.05 ) conventional, and accelerated (60,90,240; p<0.001) schedule. In our study, there are no statistically significant difference (p>0.05) level of RAI% in 6 months after second dose with compared two schedule. But it getting high level of RAI% was developed in short time (before 90 days) with the accelerated schedule than conventional schedule.Antibody titer of 2-200 RU/ ml were observed in all attendants of Selenge aimag. But only 34% of them show a protective titer. In details 62.8% of people vaccinated in 2002-2004, 55.8% of people vaccinated in 2005-2007 and 50.2% of people vaccinated in 2007-2009 year have demonstrated a protective titer. Only 21.7% and 13.4% of people vaccinated by rapid scheme and people received only first dose, respectively, have a protective immunity against TBE.Conclusion:1. The level of RAI% is increasing depends from repetition doses of vaccine TBE with accelerated and conventional schedule.2. The high level of RAI% is getting at 6 months after second dose with accelerated and conventional schedule.3. Complete dose of TBE vaccine develop a better action for establishment of specific protective immunity.