The aim of this study was to investigate the pre-service teachers' metacognitive activities occurring in the teaching scientific reasoning skills with the POE technique. The participants of the research included six pre-service science teachers who were seniors in the science education department of at a university in the west of Turkey. The holistic single-case design was used as the research method in this study. The POE Activity Report, an Activity Journal and a Semi-structured Metacognition Observation Form were used to examine the participants' metacognitive activities. Inductive and comparative analysis was used to. It was found that (i) the pre-service teachers performed various monitoring activities (f = 13) and evaluating activities (f = 4) in the teaching of six different scientific reasoning skills (control of variables, proportional reasoning, correlation reasoning, probability reasoning, combinational reasoning, hypothetical-deductive reasoning) with the POE technique; (ii) there was more variety in metacognitive activities performed by pre-service teachers in teaching of control of variables (f = 15), there was least diversity in the teaching of hypothetical-deductive reasoning skill (f = 10). The results were discussed in line with the related literature, and suggestions were presented regarding the teaching of scientific reasoning skills.