A convergent mixed methods research study was used to investigate whether or not undergraduate students who participated in a problem-based learning (PBL) laboratory environment improved their self-efficacy beliefs in chemistry. The Chemistry Attitude and Experience Questionnaire (CAEQ) was used as a pre- and post-test to determine changes in students' self-efficacy beliefs in general chemistry laboratories at a Midwestern University in the USA. Interviews were used to augment the quantitative data. Paired sample t-tests were used to determine the difference in means between pre- and post-tests. Analysis of variance was used to determine the influence of confounding variables. Thematic analysis was used to interpret the interview data. There was an observed improvement in students' self-efficacy beliefs using both qualitative and quantitative data. Interviews with the participants indicated that students had higher self-efficacy beliefs in chemistry for conducting chemistry experiments and for participating in undergraduate research after the PBL laboratory experience than they had before it. Students felt that PBL provided them with autonomy while exploring phenomena and allowed them to take more responsibility for their own learning. This study is significant in that it adds knowledge to research on the effects of PBL instruction and strengthens existing information on the relationship between PBL and the affective domain. Results from this study may also be informative to chemistry laboratory instructors on what PBL has to offer with regard to student outcomes.