Ruthenium nanoparticle tris(2,2′-bipyridyl)ruthenium(II) bis(hexafluorophosphate) (Ru(bpy)₃(PF₆)₂, RuNP) was self-assembled on polystyrene (PS) electrospun microfibers. The formation of RuNP is attributed to the sulfonated PS (SPS) microfibers' high adsorptive capability of 94% for Ru(bpy)₃²⁺, as well as the strong interaction between the Ru(bpy)₃²⁺ and ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF₆). The RuNP/SPS microfibers exhibited an enhanced electrochemiluminescence (ECL) emission, 2.3 times higher than that from Ru(bpy)₃²⁺/SPS microfibers and 6.6 times higher than that from Ru(bpy)₃²⁺/SPS continuous thin films. It is worthy of note that, as a result of the hydrophobic nature of the RuNP, the transfer of water-insoluble α-naphthol is accelerated, and thus the α-naphthol ECL quenching efficiency is enhanced. An ECL sensor based on the RuNP/SPS microfibers was fabricated and used to detect low concentrations of α-naphthol. The detection limit was of 1.0 nM (S/N > 3), and the linear response ranged from 0 to 18 μM. This sensor has been successfully applied to measure the α-naphthol content in pesticide carbaryl samples. Our work provides a very simple and cost-effective method to fabricate RuNP on polymer microfibers with great potential in the field of chemo/biosensors.