Introduction Cervical cancer and breast cancer are the major causes of mortality among women worldwide, and the burden of cancer incidence is increasing exponentially. The aim of this study was to assess the relationship between knowledge and practice of postreproductive women toward prevention and screening of breast and cervical cancer in Saudi Arabia. Methods A quantitative, descriptive, cross-sectional study was conducted using a convenience sampling method. One hundred and twenty-eight participants completed the online survey. The questionnaire consists of four main sections: sociodemographic data, obstetrical history, knowledge, and practice of breast and cervical cancer. The correlation coefficient and chi-square test were used to analyze the data. Results Nearly 40% of the participants had good knowledge of the risk factors of breast cancer; 80% had good knowledge of early warnings of breast cancer; 66% had fair knowledge of prevention measures of breast cancer; and 68% had good knowledge of prevention measures of breast cancer. Only 23% of participants had poor knowledge of risk factors of cervical cancer, whereas 62% had fair knowledge of early signs and early screening methods of cervical cancer. The majority of the respondents (85%) had good knowledge of prevention measures for cervical cancer; however, less than one-third of the participants (31%) and 39% had poor or fair practice regarding screening and prevention of breast and cervical cancer, respectively. A significant relationship between practice and knowledge was found as well as a significant relationship between practice and educational level as the p-value was less than 0.05. Conclusion Despite having a comprehensive understanding of avoidable malignancies and screening methods, postreproductive women's utilization of breast and cervical cancer examinations was inadequate. Hence, continuous awareness programs are needed to help women modify their habits and early detections.