Doxycycline hyclate was mixed with soybean oil and then added to a low-fat pelleted diet that contained approximately 2.4% fat, which produced a final diet that contained a calculated 6.4% fat and 300 mg doxycycline per kilogram of diet. The medicated diet was fed to 9 healthy adult cockatiels (Nymphicus hollandicus) for 47 days; a control group of 6 birds received the identical diet without doxycycline. Trough doxycycline plasma concentrations were measured 7 times during treatment and ranged from 0.98 to 3.83 μg/mL with an overall median of 2.09 μg/mL. The birds were observed daily, weighed, and examined at least weekly, and selected plasma biochemical parameters were measured before treatment and at days 21 and 42. No adverse effects were noted, except one treatment bird became obese. This medicated diet may be suitable for treating spiral bacteria and Chlamydophila psittaci infections in cockatiels that will consume a pelleted diet.