The Cases of xylitol poisoning in dogs are increasing as a result of ingestion of xylitol-containing products. Eighteen adult, clinically normal Pekingese dogs were orally dosed with 1 or 4 g/kg xylitol in aqueous solution. Blood samples were collected before and after dosing. Plasma insulin concentrations of both treated groups rose sharply from 20 min after xylitol dosing, peaking at 40 min. Hypoglycemia followed the increase in insulin concentration, with blood glucose values started to decrease 30 min after dosing. Other plasma biochemistry changes associated with xylitol administration were increased alanine aminotransferase and aspartate aminotransferase activities, hypophosphatemia, hypokalemia, and hypercalcemia. Plasma sodium and chloride concentrations remained normal. This study established a biochemical basis for diagnosis and treatment of xylitol poisoning in dogs.