Menarcheis the first menstruation occurred in the uterine wall and it first menstrual sign of biological preparedness, and it marks of fertility cycle has started. Preparedness of menarche shows that someone is ready to reach physical’s maturity, it is marked by a deep understanding of knowledge about the process of menstruation, so that they ready to accept and experience menarche as a normal process. Unknowing about menstruation can lead children feel difficult to accept menarche. The purposeof this research is to understanding the relationship between knowledge about menarcheand anxiety during menarche. This research is descriptive analytical method using cross sectional study, sample in this study is 48 students. The data were analyze with Spearman rank test (P < 0.05). The result of this study reveal that a half of respondents have a good degree in knowledge, 24 students (50%) and more than a half of students (52,8%) have mild anxiety. The probability test show significant value 0,000 (P<0,05). In conclusion, the results of this research is there is a relations between knowledge with anxiety when students facing menarche in elementary state 3 Bantul.