Background: Vaccination is a crucial protective intervention to prevent adult mortality and morbidity. Personal perceptions and resources have an important place in the vaccination decision. Aim: This study aimed to modify the Public Attitude Towards Vaccination–Health Belief Model scale for adult vaccines and evaluate its psychometric properties. Methods: Overall, 626 people participated in this methodological study. Content validity index, confirmatory factor analysis, internal consistency and item-total score correlation were used for validity and reliability. The independent samples t test, logistic regression analysis and ROC analysis were used for criterion and concurrent validity. Results: In confirmatory factor analysis, values of fit indices were excellent or acceptable. The Cronbach alpha value was between 0.83 and 0.92. According to criterion validity, the susceptibility, severity, benefit, and health motivation scores of those with the vaccine were higher than those without, whereas their barrier score was lower. The barrier subscale was a risk factor, whereas the benefit score was a protective factor that increased the likelihood of vaccination. The concurrent validity of the scale was tested with the COVID-19 vaccine. While the barrier subscale's ability to distinguish between vaccinated (specificity) and unvaccinated (sensitivity) individuals is excellent, it is acceptable for the other subscales. Conclusion: Modified PAVS-HBM is valid and reliable for adult vaccines. This scale was associated with vaccination behaviour and distinguished between vaccinated and unvaccinated individuals.