The objective of this study was to evaluate the effect of four different maize particle sizes in extruded diets of uniform size on kibble characteristics, metabolizability and palatability of diets for the Blue-fronted Amazon parrot (Amazona aestiva). Eight birds were allocated according to a Latin Square design (4 diets × 4 periods) which gave 8 replicates per treatment. Maize was ground with use of four different sieves (0.8, 1.2, 2.6 and 4.2 mm diameter), generating particles with different geometric mean diameters (GMD): 528, 575, 628 and 830 μm, respectively. The extruded diets had the same diameter of 7 mm. The variables evaluated were leftovers, daily intake, coefficients of total apparent metabolizability (CTAM) of dry matter (DM), crude protein (CP) acid-hydrolysed ether extract (AHEE) and gross energy (GE), as well as faecal DM content, and palatability of diets. The evaluated kibble characteristics were density, size, hardness and porosity. There was an increase in daily diet intake (P < 0.001) and reduction of leftovers amount (P < 0.001) when kibbles with maize particles with the largest GMD were fed to birds. There was an increase in CTAM of DM, CP, AHEE and GE in response to maize particles GMD increase (P < 0.05). There was also a linear increase in the density of diets with an increase in size of maize particles. Birds preferred kibbles produced with use of maize particles with GMD of 830 μm over kibbles based on particles of 528 μm GMD. It can be concluded that maize particles with the largest size (830 μm) may increase kibble density, improve feed preference and increase diet metabolizability when used in feed for the Blue-fronted Amazon parrot.