This study aims to reveal the effectiveness of redox and electrochemical cell modules based guided discovery learning on critical thinking skills and learning outcomes of senior high school students. This research is a continuation of Research and Development research, that is in the develop phase. The effectiveness test was carried out through quasi experiment with pretest-posttest control group design. The population of this study were all students of XII class at Public Senior High School 1 ( SMAN 1) Nan Sabaris, West Sumatra, Indonesia in 2018-2019 academic year. Samples were taken through simple random sampling technique. The research instruments used were a test of critical thinking skills and student learning outcomes. Critical thinking skills are analysed by percentage and learning outcomes with IBM Statistical Product and Service Solutions 23. This research found that the critical thinking skills were obtained at 92.8% in very high category and N-gain values of 0.72 in high category. It was concluded that redox and electrochemical cell modules based guided discovery learning were effective against critical thinking skills and improved learning outcomes of students in XII class at SMAN 1 Nan Sabaris. Therefore, redox and electrochemical cell modules based on guided discovery learning can be used in real learning in high schools to improve critical thinking skills and student learning outcomes.