Career maturity is one of the key aspects in understanding vocational development. It is defined as individual’s readiness for making occupational choices and it depends on their age and degree of vocational development (Savickas and Porfeli, 2011). That readiness is correlated with individual’s abilities and opportunities of their environment while being stable in time. The main goal of this paper was to validate Career maturity questionnaire (Upitnik profesionalne zrelosti – UPZ; Babarović and Šverko) and correlate it with other similar constructs. The questionnaire is a 20-item scale that forms 5 subscales: decisiveness in career decision making, active involvement in career decision making, independence in career decision making, importance of career decision making and career management, and readiness to compromises in career decision making. The sample consisted of 568 students of 3rd and 4th grade of Croatian high schools from Zagreb, Varaţdin, Zabok, Nova Gradiška and Bjelovar from the project: Vocational Development in Adolescence: Setting the Adolescent Career Transition Model. The data was gathered via online platform. The results showed expected five-factor structure of the questionnaire with good internal consistency. The results are correlated with Student Career Construction Inventory (SCCI; Savickas and Porfeli, 1983) and Career Decision Self-Efficacy Scale (CDSE; Taylor and Betz, 1983), what was a-priori expected. The results showed that UPZ and subscales of active involvement in and the importance of making a career decision are correlated with Perceived Parental Career-Related Behaviors (Dietrich and Kracke, 2009). The questionnaire showed expected gender differences but no correlation with socio-economic status. The results indicated good discriminatory power and homogeneity of all sub-scales except the subscale: readiness to compromises in career decision making which had negative correlations with other subscales and very low correlation with the overall UPZ score. Improvement of this subscale is recommended. The findings of this paper are discussed and possible suggestions for other research are given.