Subjects will be patients who are referred to the outpatient or inpatient clinic of gastroenterology departments of province level general hospitals in China. All subjects present with irritable bowel syndrome according to ROME III, and also are diagnosed with MDD by Mini-International Neuropsychiatric Interview (MINI). All subjects will provide written informed consent prior to participating in the study. Subjects will be assessed for eligibility at a screening visit, with eligible patients returning for a assessment within 1 week, at which time they will randomly enter into paroxetine CR (12.5mg/d, flexible dose: 12.5-50mg/d) plus IBS regular treatment or IBS regular treatment only. Subjects will be evaluated at weeks 2 (Day 14), 4 (Day 28), 6 (Day 42) and 8 (Day 56), for a total of 5 study treatment visits.