The early relationship between the primary caregiver and the infant begins to develop after birth, during the first year of life. The quality of the first significant relationship most likely contributes to later developmental outcomes and thus influences the individual. According to attachment theory, the quality of the early attachment relationship depends on how accessible, sensitive, and responsive the primary caregiver is to the infant's needs. If this role is fulfilled, the infant will develop a secure attachment. Maternal responsiveness is a significant predictor of the development of secure attachment in the infant, and we define it as a two-way process in which mother responds appropriately, timely, and continuously to cues expressed by the infant. Maternal responsiveness is commonly observed through the observational method, and the Maternal Infant Responsiveness Questionnaire (MIRI) is available in the literature as a subjective measure (Amankwaa et al., 2002). The aim of this study was to validate the MIRI questionnaire in the Croatian sample of mothers and fathers. The online study involved 427 mothers and 170 fathers (N = 597), who were parents of infants aged between one to twelve months. The factor structure of the questionnaire, the reliability of internal consistency, divergent validity and discriminant validity were examined. A two-factor structure of the MIRI questionnaire was determined, whereby the questionnaire consists of two independent subscales Responsiveness and Unresponsiveness. The subscales showed satisfactory internal consistency reliability and satisfactory divergent and discriminant validity. Due to its simple application, the MIRI questionnaire can be used as an instrument in further research and as part of prevention programs and other programs for parents.