The contributions of Computerized Formative Assessment (CFA) to teachers' instructional practices and students' learning outcomes necessitate the development of valid and reliable instruments for measuring teachers' literacy. To address this necessity, this study adopted an exploratory sequential mixed-methods design via drawing on a dual deductive--inductive approach to develop and validate a Computerized Formative Assessment Literacy (CFAL) questionnaire for language teachers. The participants comprised 489 Iranian male and female English as a Foreign Language (EFL) teachers teaching from elementary to advanced levels at different language institutes in eight big cities across the country. The results of Exploratory Factor Analysis (EFA) revealed that CFAL consisted of six factors including practical, theoretical, socio-affective, critical, identity-related, and developmental. The results of Cronbach's alpha demonstrated that the questionnaire and its six components had satisfactory levels of reliability. The findings are discussed and implications for developing professional programs aiming at determining and promoting teachers' CFAL are presented.