Multifunctional spherical aggregated gold nanoclusters encapsulated by polyacrylic acid/mesoporous silica shell nanoparticles (A-AuNC@PAA/mSiO2 NPs) with aggregation enhanced fluorescence (AEF) properties were fabricated by a facile and reproducible synthetic strategy. The as-prepared NPs were employed as novel theranostic agents for synergistic fluorescence/X-ray computed tomography imaging and chemo-therapy of liver cancer in vitro and in vivo.