The nature of science (NOS) is important in science teaching. Many countries embedded NOS in core curriculum documents as an essential component in science teachings such as developing conception, skill, and attitude in science in the learner. This case study was conducted at a university located in Lower Northern Thailand to explore teaching nature of science in Introductory Biology course in both lectures and laboratory sessions that were taught. Participants are three instructors (N=3) from the Department of Biology, Faculty of Science. Data were collected using qualitative instruments, including a questionnaire, semi-structured interview, classroom observation, lesson plans, and teaching materials. The results indicated that most of the instructors are strong in contents. The students put all of their focus on the teacher, and those students mostly listen, although, in activities session, students work alone. Even though some classes were questions and answers between teachers and students or discussion in the class, the instructors did not adopt the NOS in their lesson plans. Also, they used confirmatory and guided inquiry in their laboratory sessions. However, we can conclude that they used a weak and implicit approach to teach the NOS. An effective professional development program and strategies on teaching NOS at the college science level are discussed in this report.