Inclusion Criteria:

- Histologically documented colorectal adenocarcinoma

- Previous chemotherapy up to two regimens(including adjuvant chemotherapy and
first-line chemotherapy without oxaliplatin) is allowed in phase I portion; patients
are required to have discontinued chemotherapy and/or radiotherapy for at least
4weeks before entry into phase I portion. No prior chemotherapy or radiotherapy
allowed(adjuvant chemotherapy and/or radiotherapy would be allowed) in phase II
portion

- Age 18 to 75 years old

- At least one unidimensional measurable lesion using spiral CT scans (use of spiral CT
must be documented in medical records and used consistently throughout study).

- In phase I study, prior radiotherapy is permitted if it was not administered to
target lesions selected for this study, unless progression of the selected target
lesions within the radiation portal is documented, and provided it has been completed
at least 4 weeks before study entry.

- Performance status (ECOG scale): 0-2

- Patients can take food and drugs orally

- Adequate organ functions

- Life expectancy more than 3 months

- Written informed consent

Exclusion Criteria:

- Tumor type other than adenocarcinoma

- Second primary malignancy (except in situ carcinoma of the cervix or adequately
treated basal cell carcinoma of the skin or prior malignancy treated more than 5
years ago without recurrence)

- Prior chemotherapy with TS-1 and/or oxaliplatin

- Presence of CNS metastasis

- Obvious peritoneal seeding or bowel obstruction disturbing oral intake

- Evidence of serious gastrointestinal bleeding requiring transfusion

- Symptomatic peripheral neuropathy (NCI CTC v3.0 greater than Grade I)

- Major surgery within 4 weeks prior to study treatment start, or lack of complete
recovery from the effects of major surgery.

- Serious illness or medical conditions, as follows; uncontrolled congestive heart
failure, angina pectoris, arrhythmias, or hypertension, hepatic cirrhosis,
interstitial pneumonia, pulmonary adenomatosis, psychiatric disorder that may
interfere with and/or protocol compliance, unstable diabetes mellitus, uncontrolled
ascites or pleural effusion, active infection

- Pregnant or lactating woman

- Women of child bearing potential not using a contraceptive method

- Receiving a concomitant treatment with drugs interacting with TS-1 or oxaliplatin, as
follows; flucytosine, a fluorinated pyrimidine antifungal agent, phenytoin, warfarin

- Received any investigational drug or agent/procedure, i.e. participation in another
trial within 4 weeks before beginning treatment with study drug.

- Any patients judged by the investigator to be unfit to participate in the study