BackgroundThere are many different skill components used in cognitive behavioural therapy (CBT). However, there is currently no comprehensive way of measuring these skills in patients.ObjectiveTo develop a comprehensive and brief measure of five main CBT skills: self-monitoring, behavioural activation, cognitive restructuring, assertiveness training and problem-solving.MethodsUniversity students (N=847) who participated in a fully factorial randomised controlled trial of smartphone CBT were assessed with the CBT Skills Scale, the Patient Health Questionnaire-9 (PHQ-9), the Generalised Anxiety Disorder-7 (GAD-7) and the short form of the Japanese Big Five Scale. Structural validity was estimated with exploratory factor analysis (EFA) and confirmatory factor analysis (CFA), and internal consistency evaluated with Cronbach’s α coefficients. Construct validity was evaluated with the correlations between each factor of the CBT Skills Scale, the PHQ-9, the GAD-7 and the Big Five Scale.FindingsThe EFA supported a five-factor solution based on the original instruments assessing each CBT skill component. The CFA showed sufficient goodness-of-fit indices for the five-factor structure. The Cronbach’s α of each factor was 0.75–0.81. Each CBT skills factor was specifically correlated to the PHQ-9, GAD-7, and the Big Five Scale.ConclusionsThe CBT Skills Scale has a stable structural validity and internal consistency with a five-factor solution and appropriate content validity concerning the relationship with depression, anxiety and personality.Clinical implicationsThe CBT Skills Scale will be potential predictor and effect modifier in studying the optimisation of CBT interventions.Trial registrationCTR-000031307.