Objective The purpose of this study was to assess the effect of Nano-silica Coating on the Color and the Microleakage of Zirconia Ceramics. Materials and methods: Eighty-five specimens of commercially available Yttrium-stabilized-zirconia ceramics were constructed and divided into forty-five discs (8 mm in diameter) with thickness (1.2mm) They were divided into three groups (thermocycling – nano-silica surface treatment – and thermocycling with nano-silica surface treatment) to assess the color parameters, while the other forty samples were divided into ( control group – thermocycling – nano-silica surface treatment – and thermocycling with nano-silica surface treatment) to perform a fully contoured crowns to assess the microleakage. Initial color measurements were taken using a digital spectrophotometer based on CIE L*a*b* color system using a spectrophotometer Standard permanent molar tooth preparation was conducted into a full veneer preparation. Nano silica sol-gel material painted on the fitting surface of zirconia ceramics in groups of nano-silica and nano-silica with thermocycling surface treatment and processed to firing that were finally cemented on the prepared teeth using resin adhesive luting agent. Samples in aged group were subjected to 5000 thermal cycles then crown samples were sectioned to measure the microleakage. Color measurements of all samples were measured again.