Inclusion Criteria:

Patients will be included if they comply with the following inclusion criteria determined at baseline, prior to first drug administration:

• Aged over 18 years.
• Newly diagnosed or relapsing mild to moderate ulcerative colitis with disease extension beyond rectum (of at least 12-18 cm from the anorectal junction). All patients must have had at least one total colonoscopy in their disease history (within the previous 5 years).
• Disease activity will be assessed on the 7 days before inclusion and according to ulcerative colitis disease activity index (UC-DAI) score. The UC-DAI score will be from 3 to 8 (mild: 3-5 or moderate: 6-8).
• Men or non pregnant women.
• Women with childbearing potential must be using a contraceptive method judged effective by the investigator.
• Oral maintenance treatment with azathioprine or 6-mercaptopurine (taken for at least 6 months at stable dose and continued at the same dose throughout the study) is permitted.
• Informed consent given.

Exclusion Criteria:

The patients will not be included in the study if one of the following exclusion criteria is fulfilled at baseline, prior to first drug administration:

• Proctitis (less than 12-18 cm from the anorectal junction).
• Previous colonic surgery.
• Previously failed to respond to steroids within the previous year.
• Non-response to rectal 5-ASA therapy or to oral 5-ASA therapy at a dose > 3g/day for induction of remission within the previous year.
• Current relapse lasting more than 6 weeks (from what patient says).
• Severe/fulminant ulcerative colitis.
• Evidence of other forms of inflammatory bowel disease or infectious disease.
• Allergy to aspirin or salicylate derivatives.
• The following treatment will be forbidden during the study (if present at selection, a wash-out will be necessary):
• Loperamide and other antidiarrheal agents, mucilages, antibiotics: 1 week wash-out.
• Oral steroids: 4 weeks wash-out.
• Rectal steroids: 2 weeks wash-out
• Repeated treatment (> 3days of use) of non steroidal anti-inflammatory drugs (NSAID) oral or rectal route: 1 week wash-out (aspirin ≤ 325 mg/day used for cardioprotection is allowed).
• Sulfasalazine > 4g/day or mesalazine or 4-ASA at a higher dose than what is permitted in the local formulary or standard care for maintenance treatment: 4 weeks wash-out
• Immunomodulating/suppressing drugs: 3 month for wash out (except for patients maintained on azathioprine or 6-mercaptopurine -see above).
• Known significant hepatic or renal function abnormalities.
• Moderate/severe abnormal renal, hepatic or blood count tests defined as: creatinine plasma value > 1.5 x ULN or white blood cells < 3500/mm3 or > 15000/mm3 or Platelets < 100000/mm3 or > 800000/mm3 or ASAT/ALAT > 3 x ULN or GGT/Alkaline Phosphatase's > 3 x ULN (Primary Sclerosing Cholangitis is not an exclusion criteria).
• History or physical examination findings indicative of active alcohol or drug abuse,
• Pregnancy or breast-feeding,
• History of disease, including mental/emotional disorder, that might interfere with their participation in the study,
• Participation in another clinical study in the last 3 months.
• Inability to comply with the protocol requirements.
• Inability to fill in the diary cards.