The efficacy, memory, and cognitive effects of right unilateral (RUL) electroconvulsive therapy (ECT) at 2.5 times threshold in 32 inpatients with moderate to severe major depressive disorder were evaluated at baseline, during the course of treatment, and 1 month after treatment. Neuropsychological assessment included the Randt Memory Test, Personal Memory Test, short-version Wechsler Adult Intelligence Scale-Revised, and Self-Rating Scale of Memory Functions. At the treatment end point, although the Hamilton Depression Rating Scale mean score was decreased by 54.2%. the response rate of 2.5 times threshold RUL ECT using stringent criteria was only 31.2%. Treatment was associated with significant anterograde memory impairment in the short term. Mean total scores of the Randt Memory Test and Personal Memory Test were decreased from baseline by 14.8% and 32.5%, respectively, after six sessions of ECT. These memory deficits were significantly improved by the 1 month follow-up examination. Subjective memory scores increased consistently during treatment, correlating with improvements in mood. No adverse effects on nonmemory cognition were found. Although RUL ECT at 2.5 times threshold is not associated with marked or persistent cognitive disturbances, its efficacy may be insufficient in clinical practice.