The purpose of this study was to develop a valid and reliable scale for assessing high school students' self-directed learning skills. Based on a literature review and data obtained from similar instruments, all skills related to self-directed learning were identified. Next, an item pool was prepared and administered to 255 students from various high schools. To test the suitability of the gathered data, exploratory factor analysis was performed. The results revealed that there were correlations between the items, factor analysis could be conducted and nine factors were obtained. A confirmatory factor analysis (CFA) was performed concerning the quality of the factor structure. The results of the CFA confirmed the nine-factor solution. The final version of the scale has a nine-factor structure and includes a total of 40 items. This instrument uses a five-point Likert-type scale and was termed the Self-Directed Learning Skills Scale (SDLSS).