The one-phase reduction of RuCl3 with lithium triethylborohydride as a reductant in tetrahydrofuran in the presence of 1-octanethiol, 1-octadecanethiol, 1,1'-binaphthalene-2,2'-dithiol, or oligoethyleneoxythiol gave organic solvent- and water-soluble thiol-stabilized ruthenium nanoparticles. The oligoethyleneoxythiol-stabilized ruthenium nanoparticles were soluble in both water and organic solvents. The ruthenium nanoparticles were stable in the solid state and did not aggregate in solution. Transmission electron microscope images of the ruthenium nanoparticles reveal small dispersed particles with a narrow size distribution. The ligand-exchange reaction of octadecanethiol-stabilized ruthenium nanoparticles (2.0 nm) with phenothiazine-linked decanethiol afforded redox-active phenothiazine-functionalized ruthenium nanoparticles (1.9 nm) that showed a reversible redox peak at +0.51 V (vs Ag/0.1 M AgNO3) in the cyclic voltammogram.