In this work, we demonstrate a monolithic approach to fabricate free-standing LiNbO3 photonic crystal (PhC) slabs. Ion implantation is first applied to form a buried lattice-damage layer at a specified depth in bulk LiNbO3. Photonic crystal slabs are then made with FIB milling followed by wet etching. A high etching rate of 100 nm/min for the implanted layer has been obtained. A vertical PhC profile has been achieved because the bottoms of the milled cones were truncated by an air gap, with a measured slope angle of the hole sidewalls at 89°. Numerical simulation and free-space illumination measurements of the reflectance spectrum over a broadband wavelength were performed to analyse the properties of various PhC slabs. The free-standing LiNbO3 structures make them easily incorporated into MEMS and show potential applications for tunable optical filters, sensors, and quantum optics applications where high quality, single crystal LiNbO3 is needed.