To fabricate a photonic crystal with large and complete photonic bandgap, it often requires backfilling of high index inorganic materials into a 3D polymer template. However, the pore network may become disconnected before the template is completely filled in a conformal coating process, which, therefore, limits the achievable maximum bandgap in the 3D photonic crystals. Here, we demonstrate nearly complete filling of the holographically patterned, diamond-like polymer templates with titania sol−gel through the electrodeposition method. The deposition proceeded in two stages: a thin titania seed layer (∼55 nm thick) was conformally coated on the surface of the polymer template at the early stage of electrodeposition, after which the deposition occurred preferentially from the template bottom layer at a rate of ∼0.4 µm/min. After preannealing and a slow ramping rate to 500 °C to remove the polymer template, an inverse 3D anatase titania crystal was obtained without pattern collapse. The measurement of film...