Objective The goal of this study was to find out how aging and a surface treatment called sol-gel nano silica affect microleakage in zirconia ceramic crowns. Materials and methods: Twenty recently extracted human maxillary first molars were prepared for full coverage zirconia crowns made of Yttrium-stabilized zirconia ceramics that are readily available. They were split into four groups, each with five samples the control group, the thermocycling group, the nanosilica group, and the nanosilica-thermocycling group. Zirconia crown fitting surfaces were coated with a sol-gel nano silica substance. Thermal cycling was performed 5000 thermal cycles. TheraCem resin cement was used to cement all of the crowns. Crowns were submerged in 0.5% methylene blue solution for 24 hours before being sectioned bucco-lingually for microleakage testing. The depth of dye penetration was evaluated using a light stereomicroscope (Nikon MA100 Japan) at 50 magnification and image analysis software (Omnimet, Buchler, USA). The Tukey test and one-way ANOVA were used for statistical analysis. Result: The nanosilica group had the lowest microleakage, followed by the nano-silica with thermocycling group. Among the groups, the thermocycling group had the highest microleakage values. Conclusion: Although sol-gel nano silica coating reduces microleakage, ageing has a negative impact on it.