Objective: This study aims to assess the level of immunization and vaccine knowledge among high school students. Methods: The study was conducted using a questionnaire. A total of 214 highschool students participated. Immunization and vaccine related knowledge were assessed. Descriptive statistics were used to analyze the outcome of this study. Results: A total of  214 high school students participated in this study, the majority of participants were female (n=150, 70.1%). Most participants studied in grade 12 (n=129, 56.1%). Participants enrolled most in the Math-Science program (n=188, 87.9%). Parents of most participants worked as an employee (n=59, 27.6%) and the majority of monthly household income was 40,001-80,000 Baht (n=57, 26.6%). Participants learned about immunization and vaccine knowledge from social media (n=110, 51.9%). From the assessment of basic immunization and vaccine knowledge among participants, the average knowledge about immunization and vaccine knowledge score was at a moderate level (M=11.34, SD=2.43). Female participants showed a higher knowledge score (M=11.52, SD=2.20) than male participants (M=10.91, SD=2.85). Grade 12 participants showed the highest average knowledge score (M=11.64, SD=2.09) among other classes. Participants who enrolled in the Math-Science program had the highest average knowledge score (M=11.48, SD=2.43). Participants whose parents worked in Health Science revealed the highest average knowledge score (M=12.67 , SD=2.63) and the monthly household income group of <150,000 showed the highest average knowledge score (M=12.17, SD=2.04). Participants who learned about immune system and vaccine knowledge from doctors they visited for treatment revealed the highest knowledge score (M=13.00, SD=1.54). Conclusion: Immunization and vaccine related knowledge among participants was at a moderate level.