Objective: Electroconvulsive therapy (ECT) is a major treatment of catatonia; and catatonia development during electroconvulsive therapy is a highly surprising phenomenon. We present a patient with bipolar disorder who developed catatonia during ECT. Case Reports : A 21-year-old woman, with a known case of bipolar disorder in manic phase without psychotic feature, history of long acting antipsychotic use, and severe B12 deficiency, was treated with ECT. Full catatonia syndrome developed after the fifth session of ECT. Conclusion: In rare cases, catatonia can develop during ECT course in the presence of some precipitating factors. Thus, these precipitating factors should be eliminated as much as possible before the start of ECT course to prevent catatonia development.