Gamma amino butyric acid (GABA) is the major inhibitory neurotransmitter in the human brain. Alterations in GABAergic function are associated with a variety of neurological and psychiatric disorders. However, noninvasive in vivo measurement of GABA is difficult because of its low concentration and the presence of overlapping resonances. To study GABA concentration in the occipital cortex in major depressive disorder (MDD), a group of medication-naive, first episode depressed patients (n = 18, HAMD > 17), and a group of healthy controls (n = 23) were investigated using a Point Resolved Spectroscopy (MEGA-PRESS) on a 3.0 T MR scanner. The results showed that occipital GABA levels were significantly lower (P < 0.001) in the patient group than those in the healthy controls, yet the correlations between the severity of MDD (HAMD, BDI) and the GABA concentration is insignificant. Therefore, our data suggest that patients with first episode, unmedicated MDD have changes in cortical concentrations of GABA. This biochemical abnormality may be a marker of a trait vulnerability to mood disorder, and may explain the visual problem of severe MDD patients.