We present a new method to prepare TiO2 sea-urchin-like structures, which involves the initial formation of tubular nanostructures and subsequent self-assembly of the nanotubes into micrometer-scale sea-urchin-like structures. We also investigate the important role of alkali aqueous conditions in the preparation of TiO2 sea-urchin-like structures. This facile and cost-effective approach provides a new route for the preparation of self-assembled TiO2 structures. In addition, the performance of the as-synthesized TiO2 sea-urchin-like structures as the active layer of an efficient solar energy harvester is also studied and discussed.