Aim: The study aims to assess the influence of hydrothermal aging on gradient zirconia's microstructure and color stability. Materials and methods: Ten discs were constructed from gradient zirconia blanks (3Y-TZP-5Y-TZP) using CAD\CAM technology. Hydrothermal aging was done in an autoclave. Color parameters (a*, b*, L*) for each disc was measured using a spectrophotometer. In order to investigate the zirconia specimens' crystalline structure, X-ray diffraction (XRD) was performed. Color stability and microstructural changes were examined before and after the aging process. Results: Following hydrothermal aging, a statistically significant decrease in the mean (L*) value was found. However, following hydrothermal aging, a statistically significant increase in the mean (a*) and (b*) values was reported. Regarding the microstructure, hydrothermal aging did not result in any significant changes. Conclusion: Artificial aging has led to color changes in gradient zirconia that were in the clinical acceptability range, but has no impact on the microstructure of gradient zirconia.