The development of understanding of nature of science (NOS) can be seen as one of the educational goals of natural history museums. In these museums, guides take on the role of educators responsible for shaping the content and style of guided tours. They play a crucial role in making scientific knowledge and narratives accessible to visitors, leveraging their background knowledge and expertise and combining them with the exhibits found in the natural history museums. The primary goal of this phenomenographic study was to examine the conceptions held by museum guides in natural history museums regarding the integration of aspects of NOS in their guided tours. Understanding guides' conceptions is important in order to understand how reference is made to aspects of NOS during the tours. The data collection was performed via a semi-structured interviews in which guides (n = 15) were asked to discuss their approach to the integration of NOS. A phenomenographic analysis was conducted to pinpoint references to cognitive-epistemic and social-institutional aspects of science from the perspective of the Family Resemblance Approach. The analysis revealed three key dimensions: references to scientific research, references to research conducted in the museum, and references to research related to the exhibits. Within each of these dimensions are categories that illustrate the differences in their conceptions. These findings indicate that integration of NOS in guided tours is implemented primarily via implicit approach. The main theoretical contribution of this study is the conceptualization of implicit and explicit approaches to NOS integration in natural history museums.