Ideal theranostic nanoagents should be "all-in-one" type nanocrystals that have a single-semiconductor component and all-required properties (such as imaging and photothermal effects), but most semiconductor nanocrystals do not have these required properties. With SnO2 as a model of a typical wide-band semiconductor, we report the tuning from UV-responsive SnO2 to blue SnO2 nanocrystals with imaging ability and a Sb-doping-dependent photothermal effect. Sb-Doped SnO2 nanocrystals were prepared by heating SbCl3 and SnCl4 in benzyl alcohol solution through a facile solvothermal route. When the SbCl3/SnCl4 molar ratio increases from 0 to 0.2/1, the obtained samples exhibit an increased photothermal effect under the irradiation of a 1064 nm laser, accompanied by gradually decreased size and crystallinity. With a further increase of the molar ratio from 0.3/1.0 to 1.0/1.0, the resulting samples demonstrate the tetragonal SnO2 phase with amorphous-like compounds and they show no obvious enhancement of a photothermal effect. After a surface modification with biological molecules, the optimized Sb0.2-SnO2 nanocrystals demonstrated good stability and a high photothermal conversion efficiency of 48.3% as well as low cytotoxicity. When Sb0.2-SnO2 was injected into a tumor of mice, the tumor could be simultaneously detected by X-ray computed tomography (CT) and photoacoustic (PA) imaging, and then thermally ablated when exposed to a 1064 nm laser. Therefore, these nanocrystals can be used as "all-in-one" type nanoagents for imaging guided photothermal ablation of tumors under the irradiation of a laser in the second bio-transparent window.