Infiltrated liquid sensors based on a 2D photonic crystal waveguide were devised. This waveguide is designed by taking into account lowering of the radius of the central air holes in a single row and the optical resonance shifts due to refractive index change of these holes by selectively filling with different liquids. The transmission spectrum of the infiltrated liquid sensor was obtained with the use of a finite difference time domain method. At the working wavelength of 1550 nm, the waveguide mode gap edge shifts with sensitivity of 200 nm per refractive index unit. The mode gap shifts are consistent with dispersion diagrams.