The purpose of this research study was to explore the pedagogical content knowledge (PCK) of science teachers in Lebanon regarding teaching about plastic waste and plastic waste as a socio-scientific issue (SSI). SSIs are open-ended and controversial issues connected to science content. Efficacious SSI teaching is indispensable for developing scientific literacy (SL). Plastic waste, with its links to science, politics, ethics and economics, can be classified as an SSI. For the purpose of the current study’s investigation, the five PCK components from the PCK-BSSI model of Han-Tosunoglu and Lederman (2021) were considered. This research employed a case study design. Participants were ten science teachers. Data sources included interviews, classroom observations, and teachers’ lesson plans. Data were analyzed through qualitative thematic analysis. Results were compared and triangulated to increase credibility and trustworthiness of the study findings. Findings showed that science teachers’ PCK of plastic waste was characterized by low-order practices, inadequate scientific knowledge, ineffective teaching strategies, and traditional forms of assessment. The results also showed that science teachers’ PCK reflected minimal aspects of SSI. The science teachers sought to integrate disciplines, make connections to real-world problems, engage students in questioning, and involve them in discussions. Nevertheless, higher-order thinking, scientific argumentation, inquiry-based learning, and understanding the nature of science were rarely part of their lessons. In addition, the science teachers did not incorporate the political, social, ethical, and economic aspects of plastic waste into their science instruction. Although this study is limited to science teachers in Lebanon, the findings raised new questions for future research. Recommendations are provided to science educators, policy-makers, and curriculum designers.