To determine the effects of diet transition in cockatiels (Nymphicus hollandicus), 14 cockatiels were transitioned over a 12-day period from a seed diet to one of 2 commercial diets advertised as nutritionally complete. Before the transition, cockatiels were fed a seed-based diet for 30 days. The transition strategy consisted of gradually increasing the ratio of complete diet : seed-based diet over the 12-day period. True amino acid digestibility determined on each complete diet (diets A and B) demonstrated that both diets contained highly digestible amino acids. Diets differed in ingredient composition and particle size, analyzed nutrients, and method of processing (baked or extruded). Daily feed intake of seed-based and complete diets was measured. Periodically throughout and after transition, body weights were measured, and blood samples were collected for hematologic testing and plasma biochemical analysis. All cockatiels accepted the transition strategy irrespective of complete diet. Cockatiels transitioned to diet A consumed significantly more of the complete diet and less of the seed-based diet during periods of measurement throughout transition. Total feed intake was significantly greater for cockatiels fed diet B for 33% of the measurement periods (P < .05). Body weight was generally not affected during or after transition (P > .05). Hematologic and plasma biochemical values did not differ between cockatiels fed the 2 complete diets (P > .05). It may be speculated that cockatiels were more accepting of diet A during transition, and diet A more efficiently maintained body weight.