Fixed-dose combination (FDC) therapy with telmisartan 40 mg+amlodipine 5 mg (T40/A5) is expected to achieve tight blood pressure (BP) control because of the strong efficacy and long half-life of each drug. The aims of this study were to evaluate the 24-h antihypertensive efficacy of T40/A5 FDC therapy and to explore differences that may arise owing to different administration times in Japanese patients whose hypertension was not controlled by 5 mg of amlodipine per day. In this randomized clinical trial, 44 patients who had been taking amlodipine 5 mg per day and did not achieve their optimal BP target were enrolled (mean age: 67.8±10.2 years). The subjects were then randomly assigned to a T40/A5 morning or evening administration group (22 patients per group). At baseline and 8 weeks after randomization, we evaluated clinical BP and various laboratory values and performed ambulatory BP monitoring (ABPM). Clinical and mean BP evaluated with ABPM at 8 weeks (24 h, daytime, nighttime and early morning) were significantly decreased compared with BP at baseline. There were no significant differences in the diurnal BP profile change from baseline to 8 weeks between subjects in the morning and evening administration groups. There were also no significant differences in the diurnal BP profile change from baseline to 8 weeks between subjects with or without metabolic syndrome. We conclude that T40/A5 FDC therapy significantly decreased the 24-h mean and clinical BP, independent of administration time, in patients whose hypertension was not controlled by 5 mg of amlodipine.