Under the inspiration of polydopamine melanin, a new dopamine-modified poly(aspartic acid) derivative, poly(alpha,beta-(N-(3,4-dihydroxyphenylethyl)-l-aspartamide-co-alpha,beta-N-(2-hydroxyethyl)-l-aspartamide) (PDAEA), was successfully synthesized by successive aminolysis reactions of polysuccinimide with dopamine and ethanolamine. The mixtures composed of PDAEA and FeCl3 exhibited an excellent photothermal property under the irradiation of near-infrared (NIR) laser. The interactions between PDAEA and FeCl3 were investigated by ultraviolet-visible (UV-Vis) spectroscopic, Fourier transformation infrared (FT-IR) spectroscopic, and visual colorimetric measurements. Additionally, PDAEA could interact with Fe3+ in water to form spherical nanostructures with a size of 116 nm, apt to aggregate at the tumor site via the enhanced permeability and retention effect (EPR effect), implying that toxic and side effects of traditional therapy might be reduced using this method. MTT assay demonstrated both PDAEA and the obtained complex products possessed good cytocompatibility to NIH-3T3 cells (more than 90 % cell viability). The effect of photothermal therapy in vitro was also evaluated qualitatively under certain conditions using an inverted fluorescence microscope. All the results indicated that the dopamine-modified poly(aspartic acid) derivative was a promising candidate as an efficient NIR photothermal therapeutic agent for cancer therapy.