Background: Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating and changes in the consistency of bowel movements. Aim of study was to assess the effect of instructional guideline for patient with irritable bowel syndrome. Design: A quasi-experimental (pre and post) research design was used. Setting: The study was conducted at gastrointestinal outpatient clinic at Ain Shams University Hospital. Subjects: A purposeful subject of 70 adult patients diagnosed with IBS. Tools: Three tools were used for data collection. Tool (I): A structured interview questionnaire that consists of (four) parts. Part I: Patients' demographic characteristics. Part II: Clinical assessment format. Part III: Questionnaire to assess patients' level of knowledge. Part IV: Questionnaire to assess patient's health practices. Tool (II): Hospital anxiety and depression Scale (HADS). Tool (III): Pain Rating Scale. Results: The results revealed that total level of knowledge and practices scores of patients' post-implementation of instructional guidelines were improved than that of their pre-scores. It reveals that 85.7% of the studied sample had severe pain intensity pre implementation of instructional guidelines compared with 5.7% post implementation. 51.4% of the study sample had moderate level of bloating pre implementation of instructional guidelines compared to 45.7% post implementation. Also, on the effect on activity of daily living, 54.3% were moderately affected pre implementation compared to 18.6% post implementation. Moreover, there was highly statistically significant difference between them (P-value 0.000) respectively. Also, a decrease in the level of abnormal anxiety from 20% to 8.6% pre / post implementation of instructional guidelines, respectively. Conclusion: The study concluded that, application of instructional guidelines intervention for adult patients suffering from irritable bowel syndrome, reflected a highly statistically significant positive impact on patients' expected outcomes related to knowledge, health practices and reduces IBS symptoms severity compared to the previously determined percentage before implementing the instructional guidelines. Recommendations: Continuous patients' education about IBS disease should be planned regularly in outpatient clinic to control the disease symptoms and reduce its unwanted effect on quality of life.