Adolescents are individuals who experience physical changes called puberty. Menarche is the culmination of a series of primary and secondary changes as well as signs of the maturity of the reproductive organs. Providing adolescents with proper knowledge about menarche is necessary to foster their positive attitude in dealing with menarche. This study aims to determine the relationship between knowledge about menstruation and the readiness of adolescent girls to face menarche at SMPN 3 Nusa Penida. This study uses a quantitative method with a cross sectional approach. The population in this study is adolescents aged 12-13 years, with a sample of 64. The sampling technique in this study uses stratified random sampling. The research instrument used the Knowledge About Menstruation questionnaire and the Menarche Readiness questionnaire.Data analysis was carried out using the Spearman's Rho test. Research shows that most respondents have less knowledge about menstruation as many as 38 people (59.4%) and most respondents say they are not ready for menarche as many as 45 people (70.3%). The results of the Spearman's Rho test obtained a significance value of p-value = 0.000 and r = 0.810, showing a significant and very strong positive relationship between knowledge about menstruation and readiness to face menarche at SMPN 3 Nusa Penida. Respondents who have a good knowledge of menstruation will be better prepared to deal with menarche. In contrast, respondents who have less knowledge are less likely to be unprepared for menarche. With adequate knowledge support, their level of readiness in dealing with menarche also increases.