<h4>Objective</h4>To firstly examine the relationship between serum brain-derived neurotrophic factor (BDNF) levels and antidepressant response to ketamine as an anaesthesia in electroconvulsive therapy (ECT) in Chinese patients with treatment-refractory depression (TRD).<h4>Methods</h4>Thirty patients with TRD were enrolled and underwent eight ECT sessions with ketamine anaesthesia (0.8 mg/kg) alone. The gene discussed is BDNF; the disease is treatment resistant depression.