Suspended waveguides have been widely applied to silicon-on-insulator structures because they are easily fabricated with processing techniques similar to those of integrated circuit design. However, it is difficult to fabricate such structures in lithium niobate, which is also a very important material for optoelectronics. One main challenge is the difficulty of etching lithium niobate. In this work, the authors show a method to fabricate suspended slab waveguides in lithium niobate by combining ion implantation, focused ion beam milling, and selective wet etching techniques. The method does not involve wafer bonding or crystal ion slicing and is entirely monolithic. Lattice damage can be introduced to a buried thin layer of a certain depth beneath the sample surface by ion implantation, resulting in a considerable wet etching selectivity to bulk material. The etching rate has been investigated to control the size of the suspended membrane. Fabrication of suspended photonic crystal waveguides has also been demonstrated. The results show an effective method of fabricating suspended devices in lithium niobate, which enables new applications such as waveguides, modulators, and infrared detectors.