This study designed a decision-making learning module to engage students in collective decision-making in a collaborative learning environment. The purpose of this study was to explore the interplay of students' regulation learning in groups and their collective decision-making about a socioscientific issue. Thirty-eight 10th-grade students participated in the study. A variety of data were collected to examine the students' collective decision-making and regulation learning while they collaboratively conducted a socioscientific decision-making activity, including worksheets, computer activity recordings, and students' verbal interactions. The results indicated strong associations which showed that students who had sophisticated decision-making in a group tended to have more social shared regulation, and performed more regulation behaviours to refine their collective decision-making. The sequential analysis also indicated that students who manifested the serial nature of regulation processes and goal-driven learning might have exhibited a sophisticated decision-making performance when engaged in collective decision-making. The deficiencies in group interaction identified in this study underscore the need to provide scaffolds for regulation learning in order to refine students' collective decision-making in a SSI context.