Thermally-stable, ordered mesoporous anatase TiO2 with large pore size and high crystallinity has been successfully synthesized through an evaporation-induced self-assembly technique, combined with encircling ethylenediamine (EN) protectors to maintain the liquid crystal mesophase structure of TiO2 primary particles, followed by calcination at higher temperature. The structures of the prepared mesoporous TiO2 are characterized in detail by small-angle and wide-angle X-ray diffraction, Raman spectra, N2 adsorption/desorption isotherms, and transmission electron microscopy. Experimental results indicate that the well-ordered mesoporous structure could be maintained up to 700 °C (M700) and also possesses large pore size (10 nm), high specific BET surface area (122 m2 g−1), and high total pore volumes (0.20 cm3 g−1), which is attributed to encircling EN protectors for maintaining the mesoporous framework against collapsing, inhibiting undesirable grain growth and phase transformation during the calcination process. A possible formation mechanism for the highly stable large-pore mesoporous anatase TiO2 is also proposed here, which could be further confirmed by TG/FT-IR in site analysis and X-ray photoelectron spectroscopy. The obtained mesoporous TiO2 of M700 exhibit better photocatalytic activity than that of Degussa P25 TiO2 for degradation of highly toxic 2,4-dichlorophenol under UV irradiation. This enhancement is attributed to the well-ordered large-pore mesoporous structure, which facilitates mass transport, the large surface area offering more active sites, and high crystallinity that favors the separation of photogenerated electron-hole pairs, confirmed by surface photovoltage spectra.