The purpose of the study was to propose a new socioscientific issues based instruction model and to investigate the impacts of new model on PSTs? critical thinking skills and dispositions in climate change unit. Quasiexperimental method was applied. The sample of the study was determined by convenient sampling and it was comprised of 90 junior PSTs. The experimental group in which SSI based instruction was implemented, consists of 45 pre-service teachers, and there were 45 pre-service teachers in the control group. Data was gathered quantitatively with the help of Turkish version of the Ennis-Weir Critical Thinking Essay Test (E-WCTET) and the California Critical Thinking Disposition Inventory (CCTDI). Analysis of covariance (ANCOVA) was used to determine the impacts of new model on the critical thinking skills and dispositions of PSTs in experiment and control groups. Findings of the study revealed that there is no statistically significant difference between the treatment and the control group's critical thinking skills scores. However, the posttest scores of the treatment group were increased. Also, results indicated that there is a statistically significant difference between the treatment and the control group's critical thinking dispositions scores. Implications for teaching practice are discussed.