In educational reform, teaching through socio-scientific issues (SSIs) is considered the best way to promote scientific literacy for citizenship as the goal of science teaching. To bring SSIs into the science classroom, Thai pre-service science teachers (PSTs) are expected to understand the concept of SSI-based teaching and to use it effectively in their teaching. The purpose of this study is to explore PSTs' use of SSIs in their teaching during practicum, their problems with SSI-based teaching, and their professional development needs related to SSI-based teaching. The research participants were 52 PSTs in the fifth year of their bachelor's program at a Bangkok university during the 2015 academic year. The researchers collected data mainly from questionnaires, supported by classroom observations, PSTs' lesson plans, focus group interviews, and semi-structured interviews with the university supervisors and cooperating teachers. Content analysis was used for data analysis. The findings showed that most PSTs provided inquiry activity unrelated to SSIs for their students' learning. Few reported using SSIs in their teaching practices. Of those who used SSIs in their classroom, most used SSIs about health and behavior to link scientific concepts. They used video clips as the main form of media for informing students about SSIs. However, they brought in SSIs only to launch their lessons, not to drive whole lessons, and their students' role was limited mainly to discussion. They struggled with a lack of confidence in bringing SSIs into their teaching, difficulties in linking SSIs to scientific concepts, and difficulties in eliciting students' prior knowledge of SSIs. In spite of these struggles, they wanted to participate in professional development on using SSI-based teaching. These findings are significant for rethinking teacher preparation in Thailand.