Abstract This study investigates the application of silver nanoparticle (AgNPs) gel as an antimicrobial treatment to preserve wall paintings in the Palace of Prince Youssef Kamal, Upper Egypt. The wall paintings surface, susceptible to microbial deterioration were sampled, and the isolated bacteria underwent treatment with synthesized AgNP gel. The gel was produced through a two-stage process involving sonication and precipitation, yielding nanoparticles with a size range of 10–50 nm, which were confirmed by Transmission Electron Microscopy (TEM). Antimicrobial efficacy was tested through the well diffusion method, to indicate a dose-dependent inhibition of Bacillus growth, with the largest inhibition zone observed at the highest concentration (500 ppm). In addition, the study evaluated the impact of AgNPs gel on pigment stability using colorimetric measurements in the CIELAB color space. Results indicated that while most pigments retained their color, some, particularly yellow ochre and black, exhibited moderate discoloration post-treatment. These findings highlight both the potential and the limitations of AgNPs gel for conservation, suggesting its suitability for microbial control while noting the need for caution regarding pigment sensitivity.