The aim of the research was to determine the reliability, factor structure, as well as validity of the Mentalization Scale (MentS) - a self-report measure of mentalization. Two groups of subjects were examined. The first group (N = 202) consisted of students from Poznan universities; the other group (N = 229) consisted of individuals employed in various positions, with different education levels. The following measures were used: Mentalization Questionnaire, the Borderline Personality Inventory, the Experiences in Close Relationships Scale-Revised, the short version of the International Personality Item Pool NEO Personality Inventory, short version of Empathy Quotient and the Trait Emotional Intelligence Questionnaire. Reliability analysis showed high internal consistency of all three MentS subscales, and the factor analysis supports the three-factor structure of the questionnaire. Mentalization as measured by MentS was positively linked with mentalization-related constructs: empathy and emotional intelligence. Obtained relations between mentalization and attachment dimensions, borderline features and personality traits as well as observed gender differences also support the validity of the MentS. The verification of the hypotheses formulated in the present study has led to the conclusion that the Polish version of the Mentalization Scale (MentS) - a new measure of mentalization - has high psychometric value and may be used for brief yet multifaceted measurement of mentalization.