Introduction :Breast cancer is a type of cancer with the highest percentage of new cases (Kemenkes RI, 2016). Secondary prevention with early detection behavior, is considered the most rational effort to reduce mortality from breast cancer (RI Ministry of Health, 2015). The purpose of this study was to analyze the level of knowledge about breast cancer with early detection of breast cancer in women of childbearing age in Oro-oro Ombo, Ngetos District, Nganjuk District.Method :The design of this research was analytic survey with cross sectional design. Simple random sampling technique. The population of all women of reproductive age (WUS) in Oro-oro Ombo Village is 889 and a sample of 89 women of childbearing age.Data collection tool uses a questionnaire. Data analysis using chi square. Results : The analysis showed that there was a relationship between the level of knowledge about breast cancer and the behavior of early detection of breast cancer as evidenced by the statistical significance of the chi square test (χ2) and the p value velocity = 0.001.Conclusions :WUS with good knowledge of breast cancer tend to be positive (good) towards early breast cancer detection behavior. Cases of breast cancer can be immediately known at an early stage with routine early detection, so that cancer deaths can be prevented.