Aripiprazole is widely used to treat schizophrenia. Plasma levels of aripiprazole and its active metabolite dehydroaripiprazole and their clinical responses in patients were explored. Forty-five (male/female: 19/26) patients with schizophrenia were treated with aripiprazole after a washout period of at least 3 days. There was no concomitant psychotropic except benzodiazepines for insomnia. The Positive and Negative Syndrome Scale (PANSS) was used to measure the clinical response at baseline and at weeks 2, 4, and 6. Blood was drawn at week 6 to measure the plasma concentrations of aripiprazole and dehydroaripiprazole. Patients with a PANSS score that decreased by more than 20% were defined as responders after 6 weeks of treatment. There was no difference in baseline PANSS scores or the daily dosage used between responders (n = 28) and nonresponders (n = 17) (15.0 ± 5.9 vs 12.9 ± 6.9 mg, respectively; P = 0.203). The responders showed a trend toward a higher plasma concentration of aripiprazole than nonresponders (234.4 ± 156.7 vs 163.5 ± 77.2 ng/mL, respectively; P = 0.117) and a significantly higher plasma concentration of dehydroaripiprazole (101.6 ± 58.0 vs 66.0 ± 48.4, respectively; P = 0.023). Higher plasma concentrations of aripiprazole and its active metabolite dehydroaripiprazole were noted in responders than nonresponders. Compared with Western patients, Oriental patients had higher plasma concentrations of aripiprazole and dehydroaripiprazole at the same dose. We suggest that therapeutic drug monitoring of aripiprazole will help improve the response in clinical practice.