Development of a safe, efficient and inexpensive multifunctional nanoplatform using a facile approach for multimodal imaging and therapeutic functions becomes more and more practically relevant but challenging. In this work, we demonstrated a novel nanocomposites (Bi2S3-Gd) for computed tomography (CT)/magnetic resonance (MR) imaging-guided photothermal therapy (PTT) for cancer in vitro. It was achieved by modification of hydrophobic Bi2S3 with a smart amphiphilic gadolinium-chelated ligand. The as-prepared nanocomposites composed of low-cost Bi2S3 and gadolinium complexes, showed high stability, excellent biocompatibility and good photostability. It was observed that Bi2S3-Gd nanocomposites can efficiently convert the NIR light into heat, and then suppressed the growth of tumor cells under NIR laser irradiation. Apart from serving as an effective photothermal agent, the as-prepared nanomaterials could induce an efficient contrast enhancement for both CT and MR imaging at low concentrations of Bi and Gd, rendering more accurate diagnosis. This work suggests the potential of Bi2S3-Gd nanomaterials as a novel multifunctional nanoplatform for CT/MR imaging-guided PTT for cancer.