This research aims to find out how people's perceptions about effectiveness of vaccination on the level of anxiety exposed to Covid-19 which is influenced by knowledge. The sampling technique used accidental sampling. Nine districts and cities in Bali were included in the samples and 190 respondents in all. Questionnaires as research instruments and primary data are the types of data used. The Structural Equation Modeling-Partial Least Square (SEM-PLS) analysis approach was used in this study. The variables in this research consist of exogenous latent variables (knowledge), mediating latent variables (effectiveness), and endogenous latent variables (anxiety). By considering the results of hypothesis testing carried out through the bootstrapping process, the study revealed that better knowledge about Covid-19 can increase the effectiveness of vaccination by 78.9%, better knowledge about Covid-19 can reduce anxiety levels by 23.2%, increased vaccination effectiveness results in a decrease in anxiety levels by 29.4%, and better knowledge about Covid-19 can indirectly reduce anxiety levels through vaccination effectiveness by 59.3%. As a result, H0 gets dismissed in the hypothesis test, which indicates that knowledge significantly affects anxiety, both directly and indirectly through the mediation of vaccination effectiveness.