Although lessons designated for students in different fields of science, the primary objective of each course is to gain language skills to students. In this sense, each course has contributed to individuals’ mental dictionary. The purpose of this research is to determine the contribution of first-class life science textbooks to the mental dictionary. For this purpose, words and groups of words in the first-grade life science textbooks were examined. The document analyses were used in the study. The data obtained were analysed using descriptive analysis techniques, tabulated and interpreted. At the end of the research, in the first grade Life Science textbooks, it is determined that the 1039 different words or word groups are repeated 4,776 times, the number of new words is equal proportion, all of the concepts of Life Science are found, the concepts of life science are distributed in accordance with their theme, and some of the concepts are used except their themes.