One promising route to integrate nanostructured titania (NST) into nano/micro electrical mechanical systems (N/MEMS) devices is by reacting Ti films with aqueous hydrogen peroxide (aq. H2O2) solution. However, little is known about the reaction kinetics between aq. H2O2 and Ti thin films. Here, the effect of Ti microstructure and film thickness on kinetics of reaction was investigated. For films less than 50 nm thick, the kinetics is interface-reaction controlled. For thicker films, the reaction is controlled by diffusion through a hydrated titania gel layer. Activation energies of these kinetics were extracted. Pore size of NST is affected by thickness of parent Ti films. Depending on thickness of parent Ti films, NST with average pore sizes ranging from 15 nm to 150 nm was formed. The ability to form integrated porous NST features with controllable pore sizes may have implications on the development of devices for drug delivery and macromolecular separation.