This study aimed to examine the factors influencing the decision-making process of Thai Gen Y travelers in selecting online travel agency (OTA) services. The study specifically focused on demographic factors, including gender, education level, occupation, and average monthly income, and their impact on various decision-making stages: problem recognition, information seeking, alternative evaluation, purchasing decision, and post-purchase behavior. A quantitative research approach was employed, with data collected through an online survey from a sample of 400 respondents. Descriptive statistics and inferential statistics (F-test) were used for data analysis. The findings revealed that demographic factors significantly influenced decision-making processes. For instance, male respondents exhibited higher levels of post-purchase behavior compared to female respondents, individuals with education levels below a bachelor's degree prioritized information seeking more than other groups, and those with higher average monthly incomes tended to engage in more detailed and thorough alternative evaluations. These insights can be utilized by OTA providers and accommodation businesses to develop effective marketing strategies, products, and services tailored to the specific needs of target demographic groups.