Reconceptualized Family Resemblance Approach to Nature of Science (RFN) explains science as a cognitive, epistemic, and social institutional system. The aim of this study is to examine the inclusion of Nature of Science (NOS) in the 5th, 6th, 7th, and 8th grade Turkish middle school science textbooks. The "content," "activity," and "assessment" sections of each science textbook were traced based on RFN categories which are "aims and values (AV)," "scientific practices (SP)," "methods and methodological rules (M)," "scientific knowledge (SK)," and "social institutional systems (SI)" through content analysis. As a result, the total frequency value of the codes regarding RFN categories was found to be 196 in the 5th grade, 548 in the 6th grade, 284 in the 7th grade, and 427 in the 8th grade science textbooks. Most references to NOS were found in the "activity" sections of the textbooks. Although there are some references to NOS in each textbook, some of the RFN categories in the whole textbooks are missing. Furthermore, a consistent progression for the frequency of NOS related keywords was not found throughout the grade levels. In conclusion, there is a need to integrate NOS into science textbooks holistically and in a balanced way to provide a vertical articulation throughout the grade levels.