This paper reports a method to fabricate photonic crystal nickel and alumina micromechanical devices having three dimensional (3D) inverse opal microstructure. The 3D photonic crystal microstructure is fabricated using the polystyrene opals self-assembly process on gold coated silicon chips, followed by nickel electroplating. The volume fraction of these 3D nickel micromechanical devices can be controlled over the range 10% to 80%. The resulting nickel structure can be coated with an alumina shell and then sacrificed, to produce an alumina shell devices with volume fraction near 1%. To our knowledge, these are the first micromechanical devices made from a 3D inverse opal structure.