Moral sensitivity, the ability to recognize ethical issues when they arise in practice, is a key premise for career practitioners’ professional conduct of Career Guidance Counselling (CGC). Due to the diversity of ethical issues related to CGC and the situational contingency of ethical problems, the assessment of moral sensitivity is challenging. The purpose of this article is to develop a novel measure of moral sensitivity, consisting of triad judgment tasks, to assess whether career practitioners are capable of identifying ten ethical issues related to the CGC practice. In this article, we present our theoretical approach, the development phases of the Guidance Ethical Sensitivity Test (GUEST) and the first administration of the GUEST. The reliability was assessed by performing Polychoric Correlations and Categorical Principal Components Analysis (CATCPA). Administrations showed that ethics experts and most groups with ethics training scored significantly higher than others without ethics training. Future GUEST validations and implications for CGC research, training and policy are discussed.