The current research trend of metacognitive regulation has shifted from an individual to a social context. One such social context is collaborative problem-solving. Interaction between group members is an essential factor in completing collaborative problems. Metacognitive regulation is divided into four forms based on the interaction in collaborative problem-solving. This study aims to analyze the emergence and form of metacognitive regulation in groups that are more and less successful at solving geometric problems collaboratively. Each group consists of two undergraduate students who have taken geometry courses. The group tries to solve geometry problems in the form of proof problems. This study examines how metacognitive regulation emerges in group discussion activities. The emergence of metacognitive regulations was identified through student utterances when discussing in groups. In addition, interview data support researchers in exploring metacognitive regulation carried out by groups. This study also identifies forms of metacognitive regulation that occur when groups interact. The study results showed differences in the metacognitive regulation activity in four aspects: orientation, planning, monitoring, and evaluation. The more successful group has a form of co-constructed social metacognitive regulation. In contrast, the less successful group has a form of ignored social metacognitive regulation.