Background: Inflammatory bowel disease (IBD) as a chronic and debilitating disease is affected by sleep disturbance which increases the risk of malignancy. Sleep disturbance is more common in irritable bowel syndrome (IBS) and few reported studies have assessed its role in IBD. We evaluated the effect of IBS on sleep quality and quality of life (QOL) of IBD patients in clinical remission. Methods: In a cross-sectional study, 115 IBD patients in clinical remission aged from 14 to 70 years referred to gastroenterology outpatient departments and private gastroenterology offices from 2007 to 2016. Patients considered in four groups (with/without IBS). The Revised “Rome III criteria” used for diagnosing IBS. Pittsburgh Sleep Quality Index questionnaire and the health-related QOL questionnaire used for evaluating sleep quality and QOL. Results: About 85 (73.9%) cases had ulcerative colitis (UC) and 30 (26.1%) cases had Crohn's disease (CD). Forty (34.8%) cases had IBD + IBS. Poor sleep quality in UC + IBS (OR: 0.018, P = 0.003) and UC (OR: 0.016, P = 0.002) was less than CD. Diseases extent in left side colitis (OR: 0.064, P = 0.016) were less than with pancolitis. Sleep quality affected by quality of life (IBDQ) (P = 0.048). Mean quality of life (IBDQ) in patients who had poor sleep was 11% less than those with good sleep. Conclusions: The syndrome of IBS affects the sleep quality of IBD in clinical remission, especially in CD. Its additive effect with IBD may worsen symptoms that correlated with sleep disturbance, such as pain, psychological and physical condition, and QOL.