Inclusion Criteria:

- Histologically documented metastatic or recurrent gastric adenocarcinoma including
adenocarcinoma of the gastro-esophageal junction

- Age 18 to 74 years old

- Performance status (ECOG scale) 0-2

- No significant problems for oral intake and drug administration

- At least one measurable or evaluable disease defined by RECIST

- Adequate bone marrow function (ANC ≥ 1,500/uL, Platelet ≥ 100,000/ uL, Hb ≥ 9.0 g/dl)

- Adequate renal function: serum creatinine ≤ UNL (if serum creatinine > UNL,
creatinine clearance should be ≥ 60 mL/min)

- Adequate hepatic function (Total bilirubin < 2 x UNL and AST/ALT levels < 3 x UNL
without liver metastasis,total bilirubin < 3x ULN and AST/ALT levels < 5 x UNL with
liver metastasis)

- Prior systemic therapy (for instance, cytotoxic chemotherapy or active/passive
immunotherapy) is allowed if at least 6 months has elapsed between completion of
adjuvant/neoadjuvant therapy and enrolment into the study) and cisplatin was not used
before

- Patients should sign a written informed consent before study entry

Exclusion Criteria:

- Tumor type other than adenocarcinoma

- Previously exposed to any fluropymidine within 6 months before the study

- Previously exposed to Platinum therapy regardless of its period and/or duration

- Microscopic residual disease only after noncurative gastrectomy with R1 resection
(resection margin positive)

- 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 radiotherapy was administered to target lesions selected for this study, or
radiotherapy to the non-target lesions has been completed within 4 weeks before
randomization

- Presence of CNS metastasis

- Major surgery within 4 weeks before initiation of study treatment or lack of complete
recovery from the effects of major surgery (patient received curative operation or
RFA for metastatic disease)

- Serious illness or medical conditions:

- Congestive heart failure (NYHA class III or IV)

- Unstable angina or myocardial infarction within the past 12 months

- Significant arrhythmias requiring medication and conduction abnormality such as
over 2nd degree AV block

- Uncontrolled hypertension

- Hepatic cirrhosis (≥ Child class B)

- Interstitial pneumonia

- Pulmonary adenomatosis

- Psychiatric disorder that may interfere with protocol compliance

- Unstable diabetes mellitus

- Uncontrolled ascites or pleural effusion

- Active infection

- Receiving a concomitant treatment interacting with S-1 or cisplatin:

- Flucytosine (a fluorinated pyrimidine antifungal agent)

- Antivirals such as sorivudine, ramivudine, brivudine or other chemically related
agents, warfarin, phenprocoumon, phenytoin, allopurinol

- Pregnant or lactating woman

- Women of child bearing potential not using a contraceptive method

- Sexually active fertile men not using effective birth control during medication of
study drug and up to 6 months after completion of study drug if their partners are
women of child-bearing potential

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