The present study demonstrates the effect of (R)-3-oxobutyl 3-hydroxybutanoate (OBHB) on hyperketonemia in 2 patients with Alzheimer's disease dementia who were performed a mini-mental state examination score of above 11 and 10. The patients were treated with OBHB for 24 months and received usual diet. The patients were administered 15 g of OBHB three times per day for two days. The dosage of OBHB was increased to 30 g three times daily from the day 4. OBHB was always taken after adding with soda-flavoured syrups in order to mask the bitter taste. The measurement of plasma β-hydroxybutyrate (βHB) levels after every week was performed to determine OBHB plasma βHB dose-response relationships. Precision Xtra Glucose and Ketone Monitoring System (Abbott Diabetes Care, Inc., Alameda, CA, USA) was used to measure βHB levels in the blood samples. We did not observe any adverse effects of OBHB in any of the patients and it was well tolerated throughout the 24 months treatment period. Both of the patients showed marked improvement in mood, behaviour, self-care, cognitive and daily activity performance. The results revealed a marked improvement in conversation and interaction after administration of OBHB doses. The biochemical investigation of the blood samples before, during OBHB treatment and after 24 months of the treatment revealed only minor changes in the plasma lipids. There was a decrease in cholesterol level from 251 to 158 and 247 to 152 mg/dL in the two patients respectively after 24 months of the treatment. Similarly the level of high-density lipoprotein cholesterol was found to decrease from 157 to 79 and 149 to 76 mg/dL, respectively in two patients. Thus OBHB can be a promising agent in the treatment of hyperketonemia and can be taken as an oral supplement without changing the habitual diet.