A sot-gel method was developed to prepare amorphous titanium dioxide (TiO2) submicrometer sheets (a-SMSs) with regular rhombic morphology without templates. These a-SMSs comprised of primary nanoparticles, which were organized in a close packing mode in a plane. Two-dimensional (2-D) directional self-assembly of primary nanoparticles was proposed as the mechanism of forming such regular a-SMSs. It was the first time to observe such regular SMSs in amorphous TiO2, which may lead to a new scenario for colloidal particle self-assembly. After calcination at 500 degrees C, the regular shape of a-SMSs was still maintained, while the a-SMSs turned into anatase submicrometer sheets (c-SMSs), which exhibited higher activity than commercial P25 in photodegradation of rhodamine B. Furthermore, due to their larger sizes, nearly 90% of c-SMSs were readily recovered after use by centrifugation at 2000 rpm, while hardly any P25 was recovered under a similar condition.