This study aimed to test the psychometric properties of the Turkish version of the Mentalization Questionnaire (MZQ) and the mediating roles of dimensions of the MZQ in the relationship between attachment insecurity and borderline personality disorder (BPD) features. Four hundred eighty-four young adults (82.2% women, 17.8% men) aged between 18 and 37 completed the Turkish translation of the MZQ, the Experiences in Close Relationships Scale-Revised (ECR-R), the Reflective Functioning Questionnaire (RFQ), the Borderline Personality Inventory (PBI), and the Brief Symptom Inventory (BSI). Exploratory (EFA) and confirmatory factor analyses (CFA) were conducted after randomly splitting the dataset. EFA indicated a three-factor solution, and CFA supported this three-factor model, which consisted of emotional self-reflection, pre-mentalizing modes, and affect regulation. Construct validity was further established by significant correlations of the MZQ with reflective functioning and indicators of maladaptive psychological functioning. Emotional self-reflection and regulation of affect both mediated the positive relationship between attachment insecurity and BPD features. Pre-mentalizing modes moderated the relationship between attachment anxiety and BPD. The Turkish version of the MZQ can be an applicable and reliable tool for assessing mentalizing deficits not evaluated by prior tools.