TNOs (50000) Quaoar and 2002 TX300 were observed in the framework of a long-term program to study the surface properties of TNOs, Centaurs and comet nuclei using the Italian 3.58 m Telescopio Nazionale Galileo (TNG) at "El Roque de los Muchachos" Observatory (La Palma, Spain). Near-infrared spectra of both TNOs and visible spectrum of 2002 TX300 were obtained. Combining our spectra and the visible spectrum of (50000) Quaoar done by Marchi et al. (2004, A&A, 408, 17), and using the simple one-dimensional geometrical-optics formulation by Shkuratov et al. (1999, Icarus 137, 235), the visible and near-infrared spectra covering the 0.5-2.4 μ m range of both TNOs are analyzed in order to obtain mineralogical information of their surfaces. A large fraction of big water ice particles is needed to reproduce the large absorption bands observed in both objects, while other component, may be methanol, is needed to reproduce the absorption around 2.2 μ m observed in Quaoar (also reported by Brown & Trujillo 2004, AJ in press). Quaoar surface is very red, and a large fraction of complex organics is needed to reproduce the slope and general shape of the spectrum. On the other hand, the neutral color of the surface of TX300 and the huge water ice absorption bands suggest a very low abundance of complex organics. The very different fraction of tholins and water ice in the surface of both objects is indicative either of a very different original composition or a different resurfacing history. The results are discussed in the framework of the different resurfacing models already proposed. This work was supported by the grants from the National Science Foundation and the NASA Planetary Astronomy program.