Background: Minimal hepatic encephalopathy (MHE) is the mildest type of spectrum of hepatic encephalopathy(HE). Patients with MHE have no recognizable clinical side effects of HE, but have mild cognitive and psychomotor deficits .The prevalence of MHE is high in patients with cirrhosis of liver and varies between 30% and 84%. Aim of this study was to study the effect of educational guideline on nurses' knowledge regarding patients with minimal hepatic encephalopathy. materials and method: A Quasi experimental study was used in carrying out this study a convenience sample of all available nurses at the hepatology word at specialized medical hospital. one tool was used to collect data consisted of 2 parts demographic data and nurses' knowledge questionnaire sheet and three tests were used in this study (pre test, post test, after 3 months test). Results: the study results showed that there were no statistical significance between demographic data of nurses and total knowledge of nurses about hepatic encephalopathy in post test and3 months after educational guideline test. Conclusion: there was a beneficial effects of educational guideline on nurses' knowledge and there was an improvement in nurses knowledge about minimal hepatic encephalopathy after educational guideline. Recommendation: Continuous educational guideline based on the assessment of nurses' knowledge can be carried out periodically with emphasizing follow up.