Developing nano-photothermal agents (PTAs) with satisfied photothermal conversion efficiency (PTCE) in the second NIR window (1000-1350 nm, NIR II) holds great promise for enhanced photothermal therapy (PTT) effect. Herein, we develop a NIR-II PTA with advanced PTCE, based on a new two-dimensional (2D) ultrathin tellurium oxide/ammonium tungsten bronze (TeO2/(NH4)xWO3) nanoribbons (TONW NRs). The doped ammonia ions mediated-free electrons injection into the LUMO band of WO3 combined with the electronic transitions between W6+ ions and the lone pair of electrons in Te atoms achieve excellent NIR absorption of TONW NRs resulted from localized surface plasmon resonance (LSPR). The polyethylene glycol functionalized TONW NRs (PEG-TONW NRs) exhibit good stability and biocompatibility, displaying a PTCE high to 43.6%, surpassing many previous nano-PTAs active in the NIR II region, leading to remarkable tumor ablation ability both in vitro and in vivo. Meanwhile, advanced X-ray computed tomography (CT) and photoacoustic (PA) imaging capability of PEG-TONW NRs were also realized. Given the admirable photothermal effect in NIR II region, good biocompatibility and advanced CT/PA imaging diagnosis capability, the novel PEG-TONW NRs is promising in future personalized medicine application.