This study aimed to explore antibiotic knowledge, antibiotic resistance knowledge, and antibiotic use among adults in Bangkok, Thailand. This is a secondary analysis of cross-sectional data generated from a sample of 161 individuals living in Bangkok. Participants completed an online self-administered questionnaire developed by the World Health Organization. Descriptive analysis, the chi-square test, and multiple logistic regression analyses were performed. The sample comprised more females (56.5%) than males (42.2%). The majority of responders (67.7%) were between the ages of 18 and 40. More than half of the respondents mistakenly believed that antibiotics could treat colds and flu (54.7% and 47.2%, respectively). About 54.7% were aware that antibiotic resistance could harm them and their families. The chi-square test results showed that the levels of education were associated with antibiotic knowledge (p = 0.012), antibiotic resistance knowledge (p < 0.001), and antibiotic use (p = 0.023). Multiple logistic regressions showed that respondents with at least a bachelor’s degree or higher had better knowledge of antibiotics. Respondents who worked in the profession had better knowledge of antibiotic resistance. Respondents with sufficient incomes were more likely to use antibiotics. Baseline data from the study will be useful in antibiotic stewardship and public health campaigns among Bangkok residents.