Multicomponent Ni7Co3 alloy–Au nanorings can be facilely synthesized at room temperature using metallic Ni7Co3 alloy nanorings as both reducing agent and sacrificial template in water. These novel alloy–Au hybrid nanorings are well biocompatible due to coating with poly(vinylpyrrolidone) and gold nanoparticles. When increasing the molar ratio of alloy to gold salt from 1:1 to 5:1, the number of the gold nanoparticles loaded on the surface of alloy nanorings were found to be decreased, and their morphology was transformed from rod to particle, remaining the ring-like assemblies. Their saturation magnetization increased due to the ring-like assemblies, resulting in the enhancement of the signal intensity in Spin–spin relaxation time (T2) weighted magnetic resonance imaging measurement. These alloy–Au hybrid nanocomposites can perform as multimodal imaging contrast agents for cancer cell diagnosis by two-photon fluorescent imaging and T2-weighted magnetic resonance imaging. In addition, their potential application for photothermal therapy was preliminarily investigated.