Photothermal therapy (PTT) holds great promise for noninvasive cancer treatment. To fulfill this goal, highly effective and low-risk photothermal agents have been intensively explored. Here, we present a new PTT material based on conjugated polymer dots (Pdots) that exhibit strong near-infrared (NIR) absorption and high photostability. The Pdots result in a thermal response upon illumination with a NIR laser, leading to a high photothermal conversion efficiency of 65%. Thus, the photothermal ablation of cancer cells using the Pdots both in vitro and in vivo can be achieved, highlighting the potential of Pdots as a nanoplatform for clinical therapy. They also open up a new avenue to develop new photothermal therapeutic materials.