Nickel (Ni) nanoparticles with average diameters less than 5 nm were successfully synthesized on nanoporous silicon oxycarbide (SiCO) sheath−core fibers by incipient wetness impregnation of Ni acetylacetonate precursor followed by reduction at temperatures above 250 °C. The SiCO fibers were fabricated by pyrolyzing electrospun 5/15 PUS/PMMA composite fibers at temperatures from 250 to 1000 °C to contain nanoporous cores and striated sheaths. The SiCO fibers pyrolyzed up to 600 °C were superhydrophobic and became superhydrophilic when pyrolyzed at 800 °C and above. Such a drastic switch from superhydrophobicity to superhydrophilicity coincided with the disappearance of aliphatic methyl and methylene groups. The SiCO ceramic fibers pyrolyzed at 1000 °C were highly porous with BET surface area 95.7 m2/g, pore volume 0.352 cm3/g, and average pore size 26 nm. They were thermally and chemically stable enough to support the Ni acetylacetonate precursor to be reduced to Ni nanoparticles at 250, 500, and 900 °C. SEM observation and EDS elemental mappings showed the reduced Ni nanoparticles to be homogeneously distributed in the fibrous structures without any aggregation. The Ni nanoparticles were monodispersed as confirmed by TEM and in a face-centered-cubic crystalline structure as evidenced by SAED and XRD.