We demonstrate, both theoretically and experimentally, the existence of nonlocal gap solitons in twodimensional periodic photonic structures with defocusing thermal nonlinearity. We employ liquid-infiltrated photonic crystal fibers and show how the system geometry can modify the effective response of a nonlocal medium and the properties of two-dimensional gap solitons. © 2009 Optical Society of America OCIS codes: 190.4420, 190.6135, 190.4870. The study of nonlinear wave propagation in periodic photonic structures has attracted a lot of recent interest owing to the possibility of engineering both linear and nonlinear properties of the material. In such systems, self-localized beams or lattice solitons can exist owing to the interplay between effective diffraction and nonlinearity. Lattice solitons have been observed in various physical systems including optics [1] but only with on-site nonlinearity. The consideration of long-range nonlinear interactions between