AIM: To synthesize and characterize cost-efficient polyethylenimine-entrapped gold nanoparticles loaded with gadolinium (Gd@Au PENPs) for dual-mode computed tomography (CT)/magnetic resonance (MR) imaging applications. MATERIALS & METHODS: PEGylated PEI modified with gadolinium (Gd) chelator (DOTA) was used as a template to synthesize the Gd@Au PENPs and the particles were well characterized in terms of their physicochemical properties, cytotoxicity and performances in CT and MR imaging in vitro and in vivo. RESULTS: The formed Gd@Au PENPs with low cytotoxicity can be used as a highly efficient contrast agent for dual-mode CT/MR imaging of blood pool and major organs of animals. CONCLUSION: The designed Gd@Au PENPs may be used as a versatile nanoplatform for dual-mode CT/MR imaging of different biological systems.