This study aimed the development and validation of the Criminal Thinking Scale (CTS), an assessment tool for measuring criminal thinking patterns. Two hundred and seventy institutionalised inmates participated in the study by responding to a survey comprising items of the Criminal Thinking Scale developed in this study. Additionally, the Texas Christian University Criminal Thinking Scale (Cronbach’s α = .84), Early Trauma Inventory Self-Report (Cronbach’s α = .89), Parenting Style Inventory-II (Cronbach’s α = .75) were administered as well for construct validity purposes. The result of the Principal Component Analysis (PCA) confirmed the presence of three components of criminal thinking among items of the Criminal Thinking Scale which were labelled as morality averseness, rationalisation, and retaliatory reasoning with reliability Cronbach’s alpha of .87, .78, .76 respectively. The overall reliability yielded Cronbach’s alpha of .92. In addition, the Criminal Thinking Scale demonstrated concurrent validity with similar measures, that is, Texas Christian University Criminal Thinking Scale [r = .31, p < .01] and showed discriminant validity with Parenting Style Inventory-II [r = -.06, p > .05] and the Early Trauma Inventory Self-Report [r = .07, p > .05]. The study concluded that CTS is a valid and reliable measure of criminal thinking.