Impairment of neuroplasticity is considered to play a role in the pathogenesis of psychiatric disorders. To further characterize the impairment of neuroplasticity in psychiatric disorders, expression of the neuronal plasticity marker 43kDa growth-associated protein (GAP-43) was detected in postmortem hippocampal sub-regions from psychiatric patients including major depressive disorder, bipolar disorder and schizophrenia subjects, and matched control subjects. We found that GAP-43 protein levels in the hippocampal hilar region were significantly lower in bipolar disorder and schizophrenia subjects than in control subjects. We also found that GAP-43 protein levels in the inner molecular layer of the dentate gyrus and the stratum radiatum of CA2 region were reduced in a trend in bipolar disorder and schizophrenia subjects when compared with control subjects. These results suggest that impairment of neuroplasticity may occur in the hippocampus of bipolar disorder and schizophrenia patients.