Primary objective: To examine whether the switch to paliperidone ER from risperidone improves cognitive function in stabilized patients with schizophrenia.

Secondary objectives: To compare the general clinical outcomes (efficacy and safety) after switching to paliperidone ER from risperidone

This is a 12-week, randomized, parallel-group, open labeled, flexible-dose study. The patients will be randomized to the risperidone-continuation group in which they continue to receive risperidone, or to the paliperidone-switch group in which they are switched from risperidone to paliperidone. In the paliperidone-switch group, risperidone will be tapered off during the first 4 weeks of the study, while paliperidone is titrated simultaneously. The doses of both drugs will be adjusted according to the clinical judgment of each research psychiatrist, within 6 mg/day of risperidone and 12 mg/day of paliperidone.

Inclusion Criteria:

• Patients diagnosed as schizophrenia by DSM-IV-TR criteria both in inpatients
• Patients who are symptomatically stable, as judged by the treating psychiatrist, and receive a stable dose of risperidone for a minimum of 2 weeks before enrollment.
• Patients with ability to complete various questionnaires.
• Patients and/or their legal guardians/representatives who sufficiently understand the objective of the study and sign informed consent form

Exclusion Criteria:

• Active psychotic symptoms, including severe behavioral disturbance
• Relevant history of or current presence of any significant or unstable medical disease
• A woman who is pregnant, breast-feeding or planning to become pregnant during the study period
• Patients with the history of serious allergy or multiple adverse drug reactions
• Patients with the history of taking paliperidone ER within 60 days
• Patients with history of taking clozapine within 60 days
• Patients who require the treatment of other medications influencing CNS, except permitted concomitant drugs in advance