Insomnia is a common sleep problem that mothers have after giving birth. It means that the mother has trouble falling asleep or staying asleep. Aim: To determine the effect of maternal insomnia on postpartum self-care efficacy among primiparous women. Design: The research design was descriptive. Setting: The Menoufia Governorate's Kebly Maternal and Child Healthcare Center was the setting, which is in Shebin El-Kom, Egypt. The study sample consisted of one hundred postpartum primiparous women drawn from a purposive sample. An interviewing questionnaire, an insomnia assessment questionnaire, an insomnia severity index, and Orem's self-care recommendations were used to collect data. Results: There were low self-care efficacy scores among first-time mothers for meeting basic needs (97.3%), taking care of her developmental needs (82.3%), and taking care of her medical needs after giving birth (80.3%). Also, insomnia was linked to a low overall self-care efficacy score (r = 0.683), which means that the self-care efficacy score of primiparous women goes down as the severity of their insomnia increases. Conclusion: The overall self-care efficacy score of primiparous women in meeting their basic needs, developmental needs, and postnatal medical needs after giving birth was noticeably low. Also, a negative link was discovered between the overall severity of sleeplessness and the overall self-care efficacy score. Recommendations: Give all primiparous women mothering classes to teach them how to take care of themselves well after giving birth, both physically and psychologically, and provide in-service counseling programs for the primiparous women on how to reduce their degree of insomnia.