Purpose: The purpose of this study is to explore the learning outcomes of the project-based learning in a Master Class programme on sustainability carried out in collaboration by the University of Helsinki and a private company operating in global mining technology. The following two questions were addressed: Q1. What kind of sustainability competences do participants acquire in the Master Class? Q2. What is the role of PBL in the learning outcomes? Design/methodology/approach: The study is based on an ex ante open-ended survey and post-ante interviews addressed to the participants. The data were analysed using the qualitative content analysis. Findings: The findings show that the Master Class contributed to most of the competences under study. However, unlike in previous studies, systemic thinking is highlighted as a fundamental rather than a parallel core competence. Furthermore, the results also emphasise the role of emotions, which is insufficiently acknowledged and accounted for in sustainability education. Research limitations/implications: The study focussed only on the learning outcomes of the participants (students) and not the other parties (such as company and researchers). Practical implications: Future research should focus on affective dimension as a stepping stone to the transformational learning. In addition, the role of the systemic understanding in sustainability education should be highlighted as a core competence. Social implications: The study revealed the overall positive impacts of the co-creation in university-business collaboration to the participants' sustainability competences. Originality/value: The study presents an empirical case study where the various competence frameworks were applied with a result of confirming the validity of the existing key competences, in particular the systemic understanding and showing the role of the affective dimension in the transactional learning.