This study describes students’ perceptions of their physics classroom learning environments and their interactions with their teachers in upper secondary school classes in Thailand. Associations between these perceptions and students’ attitudes toward physics were also determined. The learning environment perceptions were obtained using the 35-item Physics Laboratory Environment Inventory (PLEI) modified from the original science laboratory Environment Inventory (Fraser, McRobbie, & Giddings, 1993). Teacher-student interactions were assessed with the 48-item Questionnaires on teacher Interaction (QTI) (Wubbels&Levy, 1993). Both these questionnaires have an Actual Form (assesses the class as it actually is) and a Preferred form (asks the students what they would prefer their class to be like-the ideal situation). Students’ attitudes were assessed with a short Attitude scale. The questionnaires were translated into the Thai language and administered to a sample of 4,576 students in 245 physics classes at the grade 12 level. Statistically significant differences were found between the students’ perceptions of actual and preferred environments and teacher interpersonal behavior in Thailand. Associations between students’ perceptions of their learning environment and teachers’ interpersonal behavior with their attitudes to their physics classes also were found. It was found from interviews with a sub-sample that particular categories of comments could be identified, physics being a difficult subject, evaluation and assessment not being related to the tertiary entrance examination, and teachers’ plans. These factors appear to be affecting student achievement in physics. Based on all the findings, suggestions for improving the physics laboratory classroom environment and teacher interpersonal behavior with students’ perceptions are provided.