This mixed-method study examined the influence of metacognitive awareness on the change in preservice chemistry teachers' understandings of gas behavior in the context of multirepresentational (MR) instruction. The goal was to describe the types of understanding of gas behavior held by a group of participants with high metacognitive awareness (MA) and a group with low MA before and after the MR instruction. A total of 34 preservice chemistry teachers participated in the study. Data sources included the metacognitive awareness inventory and the two-tier nature of gases diagnostic questionnaire. Data from these sources were coded and analyzed using quantitative and qualitative methods. A statistically significant difference was observed for the understanding of gas behavior before the MR instruction between the participants with high MA and those with low MA. Both groups of participants exhibited substantial progress toward a scientific understanding from pre- to post-instruction. However, the participants with high MA outperformed those with low MA in terms of developing a more scientific understanding of gas behavior after the MR instruction. In addition, following the MR instruction, while the participants with high MA eliminated 85% of their alternative conceptions, the participants with low MA eliminated only about 60% of their alternative conceptions.