Background: Hyperemesis gravidarum is often defined as intractable nausea and vomiting during pregnancy. Hyperemesis gravidarum is severe enough to affect the general condition of the pregnant women and may require hospitalization. Aim: The research aimed to investigate the effectiveness of tailored education program on pregnant women's knowledge and practices regarding hyperemesis gravidarum and on its severity. Design: A quasi-experimental research (one group pre/post-test) design was adopted to fulfil the research aim. Setting: the research was conducted at Obstetrics and Gynecology Department (high-risk pregnancy ward) and at antenatal outpatient clinics at three hospitals (Benha University Hospitals, Benha Teaching Hospital and Benha Health Insurance Hospital). Sample: A purposive sample of 120 pregnant women. Tools: Four tools were used for data collection; a structured interviewing questionnaire, women' knowledge assessment sheet, women' health practices assessment sheet and Modified 24-hour Pregnancy-Unique Quantification of Emesis questionnaire. Results: showed a highly statistically significant improvement concerning pregnant women's knowledge and healthy practices regarding hyperemesis gravidarum at post-intervention phase compared to pre- intervention phase (P≤ 0.001). There was a statistical significant reduction in the severity of hyperemesis gravidarum at post-intervention phase compared to pre- intervention phase (p≤ 0.05). Conclusion: Tailored education program and its sessions had a positive effect on the improvement of pregnant women's knowledge and healthy practices regarding hyperemesis gravidarum during pregnancy. Furthermore, there was a statistical significant reduction in the severity of hyperemesis gravidarum after applying tailored education program. Recommendations: Dissemination of the current research tailored education program to all antenatal clinics, high risk pregnancy units and maternity hospitals at Benha city.