When the spatial dimension of a material becomes comparable or even smaller than the characteristic length scale of the relevant cooperative phenomena, it is expected that all related physical properties including phase transitions of this material will be dramatically changed. In this work, we focus on the discovery, understanding, and design of low-dimensional 3d transition metal oxides (TMO). We use both physical and chemical methods including laser MBE growth, hydrothermal synthesis, and nanoparticle-catalyzed processes to grow TMO thin films and nanowires. The electronic and magnetic properties of the TMO thin films have been investigated by in-situ scanning tunneling microscopy and ex-situ SQUID magnetometer. We have observed both large-scale (over a few tens nanometers) and nano-scale electronic phase separation (PS) in epitaxially grown thin films of (La5/8-0.3Pr0.3)Ca3/8MnO3. While the large PS domains are present only below the Curie temperature, the nano-scale PS clusters exist at temperatures both below and above Curie temperature. The latter implies that the small PS may originate from doping-related disorder. The TMO nanowires of doped manganites are single crystals with tunable diameters. SQUID magnetometer and e-beam lithography prepared four-point probes have been used to study their magnetic and transport properties.