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Silica fibers were fabricated by sol-gel reaction and an electrospinning process. A high voltage source of electricity was applied to the prepared spinning solution to form the fibers. Macroporous silica fibers were prepared using polystyrene (PS) nanospheres as templates after calcination. The pore size could be controlled by adjusting the diameter of the PS nanospheres in the spinning solution. PS nanospheres with different diameters (250, 430, 600, 870, and 1000 nm) were synthesized for this purpose using the dispersion polymerization method. Silica fibers have a hydrophilic surface. A coating film applied to the fibers showed superhydrophilicity, which is not suitable for adsorbing oil contaminant. Thus, silane coupling agents containing methyl groups were used to modify the surface of the porous fibers to obtain hydrophobic and water-repellent properties. The amount of oil adsorbed by the porous silica fibers modified with various kinds of coupling agent or PS nanospheres with different sizes was investigated, to determine their effects on oil adsorption. When the size of the macropores in the fibers increased, the amount of oil adsorption increased, because oil infiltration through the pores became easier. Small hydrophobic groups of the silane coupling agent, like methyl groups, were able to adsorb more oil compared to bulky functional groups. The measured oil adsorption capacity of the porous fibers was found to be larger than that of mesomacroporous silica particles, since the voids between the fibers might provide additional space for oil adsorption.