In this study, ionic-liquid submicron particles (ILSPs) encapsulating the luminophore tris(2',2-bipyridyl)ruthenium (II) ([Ru(bpy)]) were developed as a carrier for an electrochemiluminescence immunoassay (ECLIA). The ILSPs were applied to quantitative determination of the model analyte prostate-specific antigen (PSA). The electrochemiluminescence of [Ru(bpy)] was measured with 2-(dibutylamino)ethanol as a co-reactant in nine ionic liquids (ILs). The electrochemiluminescence intensity was higher in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TFSA]) and N-(2-methoxyethyl)-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide ([MEMP][TFSA]) than the other ILs. ILSPs were prepared using polyoxyethylene sorbitan monolaurate and sorbitan monooleate as surfactants and either [BMIM][TFSA] or [MEMP][TFSA]. The [BMIM][TFSA] ILSPs had a mean particle size of 244 nm and zeta potential of - 21.0 mV, and the [MEMP][TFSA] ILSPs had a mean particle size of 293 nm and zeta potential of - 17.9 mV. Microscope images showed that ILSPs were IL-in-water emulsions that completely encapsulated [Ru(bpy)]. The ILSPs with [BMIM][TFSA] were more stable than those with [MEMP][TFSA], and [BMIM][TFSA] ILSPs was selected as a carrier in ECLIA for PSA determination. The calibration curve of PSA for ECLIA using the [BMIM][TFSA] ILSPs showed a good linear relationship (y = 0.29x + 4.02, r = 0.95) for the PSA concentration range of 100 pg/mL-100 μg/mL. The limit of detection and limit of quantification were 544 pg/mL and 35 ng/mL, respectively. Our results demonstrate that ECLIA using ILSPs can be used to easily determine the PSA concentration even with ILSPs in the particle state.