This article analyzes the implications of the use of socio-scientific issues (SSI) in a series of critical thinking competences. For this, a didactic intervention with 3 SSIs is carried out, developed during 16 weeks, in which there were 56 students who participated in a program of education in the sciences. A quasi-experimental design was used and there is a comparison of the pre-test and post-test to describe the influence of the intervention. The test information was assessed from an analysis qualitative and quantitative that compares the type of participant responses once the intervention. The study allows us to see the incidence of the SSIs in aspects, such as the acknowledgement of science as a social activity, the questioning of information, the multi-dimensional approach to the sciences, and the making of ethical judgments and fundamental decisions. In this way, this research demonstrates how the SSis for assuming scientific issues with social implications, are a possibility to motivate and promote the development of critical thinking in students of teacher training in Natural Sciences.