Science museums (SMs) are important places for informal science learning, with visitors' self-directed social interactions affecting their learning outcomes. Analyzing group conversations with varying compositions in SMs can reveal visitor interactions characteristics, knowledge construction process, and emotional experiences during their visits. This is significant for exploring how group interactions affect their learning outcomes; however, most research focuses on family interactions, with less attention given to college student groups. This study recorded and analyzed the conversations of 24 groups of college student peers in SMs to capture their social interaction characteristics and explore the relationship between interaction types and learning outcomes. Results showed that (1) conversations between college student peers in SMs were mostly perceptual talks (i.e., talks focused on directing attention); (2) different exhibit designs excelled at stimulating various interaction types: interactive exhibits mainly stimulated affective (i.e., expressions of emotions) and strategic talks (i.e., discussions on how to interact with the exhibit), whereas audiovisual and graphic exhibits tended to stimulate more connecting talks (i.e., discussions that linked knowledge and experiences); (3) the improvement of learning outcomes was closely related to connecting talks, particularly to Life connection and Knowledge connection; (4) interest development was strongly linked to strategic talks. These findings provide a basis for recommendations to effectively enhance informal learning outcomes and increase interest in informal science learning for college students visiting SMs.