The purpose of this study was to describe the changes of nurses' perceptions after introducing a 24-hour free visiting system and factors that influenced on the changes. The study was conducted at a perinatal care center in Tokyo (NICU 12 units and GCU 18 units), using a descriptive research design. The subjects of this study were 15 registered nurses who worked at GCU for at least one month before and after introducing the 24-hour free visiting system. (GCU stands for growing care units) All subjects were interviewed using a semi-constructed questionnaire. The data were analyzed qualitatively. Before introducing the 24-hour free visiting system, although most of nurses expected that it would promote "deeper relationships between parents and babies", they also had some negative feelings that it might be a cause of disturbance of "family care" and " baby care." After introducing this system, however, nurses recognized that it resulted in development of deep relationships between parents and babies as they expected. and that the concerns. which they had before introducing this system, did not happen. Two main categories of factors related to these changes of nurses' perceptions were identified: factors related to nurses themselves and those related to surrounding environment (or working climate). Factors related to nurses themselves were "years of experiences," "belief of relationship between parents and babies," and "recognition of the real numbers of the visitors." "Relaxed space" and "educational intervention to parents" were included in factors related to working climate. Finally, several implications for clinical practice were identified.