In this research, it is aimed to develop a “Digital Security Self-Efficacy Inventory” to determine the digital security self-efficacy levels of secondary school 7th students. First of all, a 52-item article pool was created by scanning the Social Studies Curriculum and Information Technologies and Software Course and related literature. As a result of expert opinions, necessary arrangements were made, and 7 items were excluded from the scope, and a 45-item inventory consisting of 5 subscales of the five-Likert type was developed. The sub-scales consisted of technical, psychosocial, online shopping, rights and responsibilities, and health sub-scales, respectively. Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were performed for the validity and reliability studies of the inventory, and for these studies, data were collected from 1174 secondary school 7th grade students in total. As a result of the EFA, 5 items from the technical sub-scale were removed from the scale, and a structure consisting of 15 items and 2 factors explaining 32.86% of the total variance was revealed. Psychosocial sub-40,33 percent of the total variance in the scale that explains the 8-point one-factor structure, online shopping sub-5 percent of the total variance in the scale that explains 49,79-item, single-factor structure, rights and responsibilities of the sub-44,32 percent of the total variance in the scale that explains a 7-point single-factor structure and health sub-scale of the total variance in 49,81 5% that explained the single-point-factor structure was revealed. As a result of the CFA, the model fit indices obtained for the subscales are at an acceptable level, and the structure is theoretically and statistically confirmed. As a result of the reliability studies, Cronbach's Alpha reliability coefficients were calculated as 0.85 on the technical sub-scale, 0.77 on the psychosocial sub-scale, 0.78 on the online shopping sub-scale, 0.78 on the rights and responsibilities sub-scale, and 0.75 on the health sub-scale. According to the results of the analyzes, the digital security self-efficacy inventory, which consists of 40 items and 5 subscales developed for secondary school 7th grade students, has proven to be a valid and reliable measurement tool.