This trial is to investigate efficacy and safety of YKP10811 in Subjects With Irritable Bowel Syndrome With Constipation. The difference of responder rate between test group (10, 20 and 40mg) and placebo will be evaluated.

Inclusion Criteria:

1. more than 18 years old
2. patients met with ROME III criteria for C-type IBS

Exclusion Criteria:

• pregnancy or lactation
• a history of surgery for gastrointestinal tract
• a history of gastrointestinal bleeding, diverticulitis and ileus within 1 year of screening visit
• inflammatory bowel disease or malignant tumor within 5 years of screening visit
• taking drugs that could have impact on efficacy assessment