In the pursuit of novel multimodal nanoprobes, the application of superparamagnetic gold‐coated iron oxide nanoparticles (NPs) of 6 nm as contrast agents in phantoms for X‐ray CT, US, and T2‐weighted MRI is tested. It is hypothesized that the gold coating could increase the contrast of these NPs when irradiated with X‐rays. The impact of the surrounding environment in the attenuation of gold coating is also evaluated by performing the measurements in air or in water to better mimic in vivo conditions. Additionally, it is proved that these NPs can enhance contrast in ultrasound scanning. Furthermore, their magnetite content is a known source of negative contrast in MRI. As expected, for the X‐ray CT phantoms, there is a linear increase of contrast with concentration. Additionally, the attenuation of gold in water is lower than that of the same sample in air, and the rate of attenuation at different voltage varies differently depending on the surrounding media. Interestingly, it is possible to obtain brighter ultrasound images by using these NPs and their ultrasound signal increases with the concentration of the particles. Moreover, and as expected, T2‐weighted MRI images become substantially darker as the concentration of iron increases. The obtained results and their comparative analysis show that these kinds of NPs can effectively be used as contrast agents in MRI, CT, and US. This could be an interesting starting point for future applications as multimodal contrast agents for targeted imaging. The application of gold‐coated iron oxide nanoparticles as trimodal contrast agents for MRI, X‐ray CT, and US is presented. Phantoms of different concentrations are measured in all three modalities at the same concentration for comparison purposes. Additionally, the effect of the energy of X‐rays and the surrounding media of the samples is evaluated.