Design of heterostructured TiO2-SiO2 fibers with desired porous hierarchy holds exciting implications for applications such as optoelectronics, adsorption, sensing and catalysis. The current work demonstrates for the first time that the porous hierarchy of TiO2-SiO2 fibers can be regulated based on the hydrolysis and polycondensation of inorganic alkoxides. The fabrication of porous TiO2-SiO2 fibers is accomplished by single-spinneret electrospinning without using sacrificial templates and special heat treatment. The TiO2-SiO2 composite fibers with narrow mesopores, meso-macropores and micro-meso-macropores have been obtained, and the factors governing the porous hierarchy have been investigated. The presence of Ti-O-Si linkages and the interfaces between amorphous and crystalline domains are evidenced by XPS and high magnification TEM. Mesoporous TiO2-SiO2 fibers exhibit excellent photocatalytic activity in the degradation of Rhodamine B comparable to Degussa P25. The photocatalytic activities of the TiO2-SiO2 fibers may be attributed to the combined merits of mesoporosity, high specific surface area, good adsorption capacity for Rhodamine B and anatase-rutile heterojunction. The current contribution unveils the potential of the hydrolysis and polycondensation chemistry of inorganic alkoxides in the design of heterostructured inorganic fibers with desired porous hierarchy for advanced applications.