The nanocarrier-based delivery system has emerged as a promising candidate for cancer therapy; nevertheless, their quality problems, variation between batches, and carrier-related toxicity issues have restricted their clinical utilization. Compared with traditional carrier-based nanoparticles, carrier-free nanodrug delivery systems preferred to overcome all these drawbacks and will have a wide range of applications in biomedicine and nanotechnology. Herein, we developed a novel carrier-free nanodrug Asp-UA consisted of the classical drug aspirin and the natural plant drug UA via a green and simple approach. The Asp-UA NPs were investigated for shape, particle size, zeta potential, stability, and UV-vis spectroscopy absorption. Cellular uptake study showed that Asp-UA NPs could be easily internalized by HepG2 cells; cellular study demonstrated that Asp-UA NPs held better inhibitory efficiency on tumor metastasis with low toxicity in vitro and in vivo. Moreover, Asp-UA NPs could obviously suppress the progress of cancer metastasis by H22 cells in vivo. Overall, Asp-UA NPs possess a variety of advantages and hold promise to become an alternative to the treatment of cancer metastasis.