Pain can be managed by using both pharmacological and non-pharmacological methods. The nonpharmacological method used is breastfeeding for managing pain and it is the preferred method during infancy. The aim was to identify the effect of breastfeeding on immunization pain intensity level among infants. Subjects and method: Design: A quasi-experimental research design was used to fulfill the aim of the current study. Setting: the research was conducted in the Maternal and Child Health Center (Dar El-salaam Abdallah). Subjects: A purposive sample of 200 mothers and their infants was included and assigned into control and study group, 100 infants in each group (100 breastfed before, during, and after immunization and 100 not breastfed). Two tools were used: Tool (I) A structured interview questionnaire and Tool (II) Neonatal Infant Pain Scale. Results: The results revealed that majority of the infants in the study group their facial expressions were relaxed, half of them did not cry at all, and the breathing pattern was relaxed among 66% of them. Highly statistical significance differences between infants six behavioral pain indicators including facial expression, crying, breathing pattern, arms, legs, and state of arousal in the study group and control groups. There were significant differences between pain scores of the infants after immunization in the study and control groups (at P<0.0001). In study group, more than half of infants had no pain compared to all infants in the control group who felt pain. Conclusion: It was concluded that breastfeeding was had highly statistically significant positive effect non-pharmacological method for reducing immunization pain intensity level among the studied infants in the study group versus control group. Pain intensity was significantly less among the infants administered immunization during breastfeeding. Recommendations: It is recommended to use breastfeeding during immunization as an intervention to reduce pain among infants. It needs less time, minimum effort, and is cost-effective without side effects which can be used easily in clinical settings. Replication of the current study with a larger sample of infants in different settings is required for generalizing the results.