Schizophrenia is compromised of several debilitating symptoms. Antipsychotics offer an effective treatment for positive symptoms, while the negative sign and cognitive deficits are usually treatment-resistant. It was suggested that glutamate dysregulation may be involved in the neuropathology of schizophrenia, mainly through NMDA dysfunction. We hypothesized that addition of memantine, a weak non- selective NMDA receptor antagonist approve for dementia, to antipsychotics would improve the clinical status of un-remitted schizophrenia patient, notably the negative sign and cognitive deficits. in this double- blind, placebo controlled study, participants (59 patient ) were assigned to receive placebo or memantine (once daily), in dosing titration as follows: week 1, 5mg/day; week 2, 10 mg/day; weeks 3-8, 20 mg/day, in addition to continuing tretment with antipsychotics for 8 weeks. The primary efficacy measures was the total score on positive and negative symptom scale (PANSS) and secondry outcome.