Background: The nature of the oral environment is very complex which promotes wear and surface roughness of dental restorations, consequently altering function and esthetics. Therefore, the wear and surface roughness of recently introduced gradient zirconia are under investigation. Aim: to evaluate wear and surface roughness of cubic and gradient zirconia under simulated oral conditions Materials and methods: Twenty-four disc-shaped samples (10mm X 2mm) were designed and milled using CAD/CAM. They were divided into two equal groups (n=12) according to the material type: Group C: Cubic zirconia (BruxZir Esthetic) and Group G: Gradient zirconia (IPS e.max ZirCAD Prime). Finishing and polishing of all samples were done then baseline weight values were obtained by an electronic balance followed by baseline surface roughness measurement using a 3D non-contact profilometer. ROBOTA chewing simulator was used to apply a 5kg (49N) load for 75000 cycles representing six months of clinical function, with a vertical movement of 1mm and a horizontal movement of 3mm. Weight values were re-measured as an indication of weight loss. Further measurement of Surface roughness was obtained to evaluate the surface changes. Results: Mean and standard deviation values (± SD) of weight loss and surface roughness before and after wear for group C and group G using independent t-test revealed a statistical significant difference for each group as P