Background This study evaluated the effect of air-particle abrasion with different particle sizes on the surface roughness and phase transformation of yttria-stabilized tetragonal zirconia ceramics (Y-TZP). Methods Eighty-four Y-TZP discs of 15mm diameter and 1.0mm thickness were fabricated. The samples were divided into four groups (n=21): (1) air-particle abrasion with 30m CoJet sand blast coating agent (CoJet, 3M ESPE); (2) 50m Al2O3 particles; (3) 110m Al2O3 particles; and (4) 250m Al2O3 particles. Each group was further divided into three subgroups each (n=7) and treated for 5seconds, 15seconds and 30seconds. Mean surface roughness was determined using a profilometer. The surfaces were analysed with a scanning electron microscope. XRD analysis was employed and the relative amount of the monoclinic phase was calculated. The results were statistically analysed by two-way analysis of variance (ANOVA, p<0.05). Results Air-particle abrasion with 250m Al2O3 particles for 30seconds had the highest surface roughness (p<0.001) and a significantly higher amount of monoclinic phase compared to air-particle abrasion with 30m, 50m and 110m particles (p<0.001). Conclusions Duration and particle size of air-particle abrasion affects the roughness and phase transformation of Y-TZP. Longer treatment times with larger particles may result in degradation of material.