A hierarchically porous layered lithium-rich oxide, 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2, is synthesized by co-precipitation of metal oxalates with an assistance of a moderate polyethylene glycol (PEG2000). The morphology and crystal structure of the product are characterized by scanning electron microscope, transmission electron microscopy and X-ray diffraction, and its performance as cathode of lithium ion battery is evaluated with charge/discharge tests. It is found that the as-synthesized oxide exhibits excellent rate capability and cyclic stability: delivering an initial discharge capacity of 262 mAh g−1 at 0.1C (1C = 250 mA g−1) and 135 mAh g−1 at 4C, and possessing a capacity retention of 83% after 200 cycles at 4C. These performances can be attributed to the unique structure of the as-synthesized oxide: uniform secondary microspheres of about 10 μm, which is composed of uniform primary microparticles of about 2 μm, and hierarchically porous structure with pores distributed among primary and secondary particles. The hierarchically porous structure provides large reaction sites for lithium ion insertion/extraction and large space to buffer the volume change during cycling, leading to the excellent rate capability and cyclic stability of the as-synthesized oxide.