A new photothermal coupling agent for photothermal ablation (PTA) therapy of tumors is developed based on ultrathin PEGylated W18O49 nanowires. After being injected with the nanowire solution, the in vivo tumors exhibit a rapid temperature rise to 50.0 +/- 0.5 degrees C upon irradiation with NIR laser light at a safe, low intensity (0.72 W cm(-2)) for 2 min (left-hand mouse in the figure),), resulting in the efficient PTA of cancer cells in vivo in 10 min.