Brain-derived neurotrophic factor (BDNF) plays an important role in the pathophysiology of bipolar disorder. Some clinical studies indicate the blood BDNF level decreased during the depression phase in the bipolar disorder, and the blood BDNF level is negative proportional to the severity of the depression; and the same phenomenon was found, i.e. the blood BDNF level decreased during the manic phase in the bipolar disorder, and the blood BDNF level is negative proportional to the severity of the mania. Quetiapine fumarate was found to reduce the decreasing of the expression of BDNF in the rat hippocampus and brain mantle in some animal experiments, indicating quetiapine fumarate has the possibility on potential interfering BDNF in the treatment. However, few study on comparison of the blood BDNF level between pre and post treatment in the bipolar disorder was conducted.