Background: Irritable bowel syndrome is a functional gastrointestinal disease that can cause distress and affect individuals' abilities, productivity and even quality of life. Lifestyle modification is a significant strategy to promote health behaviors, manage symptoms and lessen disease episodes. Aim: to examine the effect of Pender's model guided lifestyle modification on reducing of irritable bowel syndrome episodes among adult females. Design: A quasi-experimental design (pre/ posttest) was operated for current study. Setting: The current study was done at internal medicine outpatient clinic at Shebin El Kom Teaching Hospital in Menoufia governorate, Egypt.  Sample: A purposive sample of 100 adult females diagnosed with irritable bowel syndrome was enrolled in this study. Instruments: Two instruments were used I:  Structured interviewing questionnaire involved three parts of Pender's model as individual characteristics and experience, behavior specific cognitions and affect, and health promoting behaviors. II-Severity Symptom Scale. Results: After three months of application of lifestyle modification intervention, 77.0% of studied female had good knowledge compared to 10% pre intervention and knowledge total mean score was increased to 23.7 compared to 12.6 pre intervention. Total symptoms severity mean score among the studied females was decreased from 283.41±85.74 to 175.78±89.42 post intervention. Also, after intervention, a highly statistical significant improvement was noticed among studied females in relation to total mean score of health promoting behaviors than before intervention as P<0.001. In addition, a statistical significant correlation was observed between symptom severity and Pender's model components as P<0.001  Conclusions: Application of lifestyle modification intervention based on Pender's model had a substantial effect on increasing knowledge, improving symptoms, and succeeded in reducing episodes of irritable bowel syndrome among adult females. Recommendation: Frequent educational program should be implemented regularly at outpatient clinic to raise patients^, awareness regarding irritable bowel syndrome episodes and its management.