Sputter deposition of metals in a capture medium with extremely low vapor pressure is a simple and convenient method to generate metal nanoparticles (NPs) without chemical reactions. By careful selection of the capture medium and/or temperature of the medium for the deposition, the size of the synthesized NPs can be controlled. Sputtering conditions also play an important role in determining the size of the NPs. We synthesized Au NPs in a standard ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim]BF₄) by systematically varying the sputtering conditions, which influence the formation processes and/or the size and size distributions of Au NPs. The Au NPs were characterized by small-angle X-ray scattering immediately after the synthesis of NPs in the capture medium. It is concluded that the temperature of the target and applied voltages have a strong influence on the size of Au NPs generated in the capture media, while the working distance between the target and the surface of the capture media, sputtering time, and discharge current have little or no influence. Lower temperature of the target and higher applied voltage are desired for generating size-controlled smaller NPs.