The aim of this study is to investigate the computational thinking skills of secondary school students and their perceived self-efficacy related to block-based programming. The study group consists of 464 students attending 5, 6, 7, and 8 grades in a province located in the Central Anatolia region, Turkey. Data were collected by Computational Thinking Skills Scale and Self-Efficacy Perception Scale related to Block-Based Programming. Independent sample t-test was used for comparisons of gender, programming education, Scratch and Arduino learning status apart from lessons. According to the findings, it was determined that the computational thinking skills of students were high. Significant differences were found in both computational thinking skills and self-efficacy perceptions of block-based programming according to gender, programming education, and Scratch and Arduino learning status.