Abstract: It is crucial to obtain nano-humic acid solubility data in urea aqueous solutions for the production of nano-humic acid added urea. Solubility and density of nano-humic acid in urea aqueous solutions at 298, 303 and 308 K were experimentally determined by an isothermal solution saturation method and phase diagrams of the ternary system were obtained. Equilibrium solid phase compositions were identified by combining wet slag and X-ray diffraction (XRD) methods. The results show that there are four phase zones in the ternary systems including nano-humic acid and urea pure solid phase crystallization areas, co-crystallization zone and unsaturated zones of nano-humic acid and urea. The ternary system shows simple saturation and no solid solutions are formed in the system. The phase diagram of 308 K shows larger co-crystallization zone than those of 298 K and 303 K. The maximum density at co-saturation sites are 1.2145, 1.2333 and 1.2502 g·cm^-3 under 298, 303 and 308 K, respectively.