Background: Family planning (FP) is an important component of reproductive health (RH). Through FP, couples can plan the number and spacing of their children. The objective of the study was to assess the knowledge of women about the use of FP services. Methods: A quasi-experimental study was conducted at FP clinics in health care centers and units in Mansoura District. Data were collected from 415 married women selected by systematic random sampling technique from the selected FP clinics according to the proportionate client flow. The data collection tool included a self-structured questionnaire assessing the knowledge of women. Analysis was done using descriptive and inferential statistics. Results: The mean age of women was 36.93± 7.4 years. The majority of women were rural residents (76.9%), married (88.4%), participants are educated up to secondary school (87%), and working (88.4%). The majority of women had fair (98.2%) or poor (10.4%) knowledge about the use of FP services at the pre-test. A statistically significant improvement in knowledge score was observed at the post-test (good knowledge increased from 1.4% to 100.0%, p < 0.001). In multivariate analysis, age, monthly income, and social score were significant predictors of knowledge improvement (p < 0.05). Conclusions: Knowledge score can markedly improve after appropriate health education. Women with older age, lower monthly income, and higher social score have better knowledge improvement. Therefore, it is recommended that future studies to improve the knowledge of women toward the use of FP services through comprehensive health education programs using different methods.