This study aimed to develop and validate the Sustainable Behavior Questionnaire (SBQ), a comprehensive tool for assessing environmentally sustainable behaviors among Italian adults. Drawing on established theories and scales, the SBQ was refined through a two‐part study. Study 1 involved reviewing the literature, selecting items, and conducting exploratory factor analysis (EFA) on responses from 219 participants. This process resulted in a four‐factor structure: “purchase behavior and awareness,” “reusing and recycling,” “reducing,” and “walking” and “use of public transport.” Study 2, comprising 432 participants, confirmed the four‐factor structure through confirmatory factor analysis (CFA) and established the SBQ's convergent validity with Intention Sustainable Behavior (ISBQ) and Environment Sustainable Value and Norms (ESVN) measures. The SBQ demonstrated robust internal consistency, providing a reliable instrument for assessing sustainable behaviors. This research contributes to the field by offering a psychometrically sound questionnaire for evaluating sustainable behaviors among Italian adults and further understanding their role in promoting environmental conservation and well‐being.