Electrodeposition of platinum (Pt) from bis(acetylacetonato)platinum(II) (Pt(acac)2) has been investigated in bis(trifluoromethylsulfonyl)amide (TFSA-) ionic liquids composed of 1-butyl-1-methylpyrrolidinium (BMP+), 1-hexyl-1-methylpyrrolidinium (HMP+) and 1-decyl-1-methylpyrrolidinium (DMP+). Pt(acac)2 was found to be electrochemically reduced to Pt(0) in each ionic liquid. Reduction of Pt(acac)2 was suggested to involve formation and disproportionation of some intermediate species of Pt by cyclic voltammetry. Potentiostatic cathodic reduction at -1.7 V resulted in deposition of Pt and Pt nanoparticles dispersed in the ionic liquid. The average sizes (in diameter) of the Pt nanoparticles were found to be 2.6 ± 0.7, 4.1 ± 1.2 and 4.3 ± 0.7 nm in BMPTFSA, HMPTFSA and DMPTFSA, respectively. The average particle sizes of the Pt nanoparticles tended to increase with an increase in the alkyl chain length of the cations of the ionic liquids.