Teachers' beliefs are strong predictors of their practices. They guide how teachers understand the implementation of effective inquiry-based lessons. The cross-case analysis indicated that the fundamental problems observed in many Thai pre-service science teachers' classroom inquiries stemmed from their beliefs on teaching science. Although the teachers agreed on the importance of having students engage in scientific inquiry through hands-on activities, they believed that its purpose was to help students' sense-making of what the teachers told them. They believed an emphasis should be placed on asking as many knowledge questions as they would like, providing answers, giving procedural instructions to students, and offering specifics of what students should observe in the hands-on activities. The teachers believed that these were effective avenues to help students gain scientific knowledge in terms of concrete experiences. The observed lessons evidenced that teachers failed to elicit students' interest, curiosity, and engagement in inquiry lessons. This study suggests that pre-service teachers benefit from being provided with real-world opportunities to reflect on their educational beliefs and get suitable supports to transform their beliefs for delivering inquiry-based science lessons.