Currently, one of the major hurdles hindering the clinical applications of photothermal therapy (PTT) and photothermal-chemo combination therapy (PCT) is the lack of highly efficient, readily derived, and irradiation-safe photothermal agents in the biologically transparent window. Herein, we report the first design and rational construction of 0D/2D/0D sandwich heterojunctions for greatly enhanced PTT and PCT performances using 0D N-doped carbon dots and 2D MoS2 nanosheets as the assembly units. The well-matching heterojunctions enabled an additional enhancement in NIR absorbance owing to the carrier injection from carbon dots to MoS2 nanosheets, and achieved a much higher photothermal conversion efficiency (78.2%) than that of single NIR-CDs (37.6%) and MoS2 (38.3%) only. In virtue of the heterojunction-based PTT, complete tumor recession without recurrence or pulmonary metastasis was realized at an ultralow and safe laser exposure (0.2 W cm-2) below the skin tolerance irradiation threshold. Furthermore, by taking advantage of the strong X-ray attenuation and effective drug loading capacity of MoS2 nanosheets, the CT imaging-guided PCT was achieved at 0.1 W cm-2, without inducing noticeable toxic side effects. Our findings can substantiate the potential of a novel 0D/2D heterojunction for cancer theranostics.