In this research, it was aimed to determine the relationship between critical thinking skills and mathematical problem solving achievements of the secondary education students. Descriptive screening model was determined as the method of the research. The study group of the research included totally 429 students chosen randomly among the secondary education students studying at the 5th, 6th and 7th grades of state schools affiliated to Adana province Seyhan district National Education Directorate in 2018-2019 academic year. As data collection tools, "Critical Thinking Scale" developed by Görücü (2014) in accordance with the level of secondary education, and "Problem Solving Success Determination Test" developed by Kösece Logoglu (2016) were used. Data were analyzed in SPSS 22.0 statistical software. As a result of the analyses, it was determined that there was a positive significant relationship between "looking for the truth" and "communication" subdimensions of problem solving achievements and critical thing skills scale. In accordance with the results obtained from the study, considering the suggestions below was remarkable in terms of improving critical thinking skills and mathematical problem solving success of the secondary education students: The lessons should be lectured with activities related to getting the students acquire a critical point of view for solving the mathematical problems. The studies of establishing problems should also be carried out besides the studies of solving mathematical problems for the students. The teachers should primarily be individuals who can think critically for getting students acquire critical thinking skills, and necessary training should be provided for providing teachers to acquire this skill.