Aims: To investigate the effect of mechanical and chemical surface treatments including (AL 2 O 3-110µm) and citric acid solution (30%) on the microhardness of zirconia ceramic. Materials and Methods: Twenty four cubic shaped specimens were prepared from partial sintering zirconia (IPS e.max ZirCAD MT).Specimens were randomly assigned into three main groups (GI, GII, and GIII) according to the surface treatment methods (n=8). Group I: zirconia surface left without surface treatment (control), Group II: In this group all specimens were subjected to sandblasting with 110 µm Aluminum oxide particles (Al2O3), while Group III: The surface was treated with citric acid solution 30% for 10 minutes. Force of Vickers microhardness was applied on the intaglio surface of the zirconia specimen at 0.5 kg for 30 seconds. Data were analyzed with one way ANOVA at 5% level of significance. Results: Sandblasting with AL2O3 110µm significantly increased the Vickers microhardness value of the zirconia surface. Chemical treatment with 30% citric acid did not exhibit any significant changes in comparison to the control group. Conclusions: Within the limitation of this in vitro study, the mechanical surface treatment of the zirconia surface with AL2O3 improves the surface microhardness.