Introduction: The purposes of this study were to explore the factors that motivated and those that discouraged students from speaking English outside of the classroom at Asia-Pacific International University, Mauk Lek Campus. The university offers undergraduate programs in both English and Thai medium. The majority of Thai students who were enrolled in both programs notably lived in the University dormitories, which exposed them to students from 32 different countries, yet were still hesitant to speak English. Methods: Using the convenience sampling method, 197 students were selected to participate in this study. A descriptive quantitative method and a self-administered questionnaire were used to collect the data. Result: The findings reveal that motivation for speaking English outside the classroom was mainly for instrumental motivational reasons (M=4.17, SD=0.59), followed by integrative motivational reasons (M=3.74, SD=0.67). Less clear reasons were intrinsic motivation (M=3.41, SD=0.75) and extrinsic motivation (M=3.32, SD=0.82) motivations. The study also reported that factors such as inadequate vocabulary to speak effectively, insufficient knowledge of English grammar, and inability to speak English fluently and continuously, were perceived as hindering them from speaking English outside the classroom. Lastly, the study found statistically significant differences at the 0.05 level in instrumental motivation, intrinsic motivation, and extrinsic motivation when compared with gender, faculty, class status, program of study, and period of learning. Discussion: The recommendations for future research threefold: to study learning approaches to a variety of vocabularies which would enhance students’ communication outside of the classroom; to study participants from other nationalities; and to use a larger sample using other types of sampling and data collection methods.