Thiol-capped metal nanoparticles have two constituents: an inorganic metal and an organic molecule as a shell. Both characters are inbuilt in the structure of the metal thiolate. Herein, we have investigated bismuth dodecanethiolate as a precursor for the synthesis of dodecanethiol-capped bismuth nanoparticles (Bi NPs) by a solid-state grinding method. By using sodium borohydride and bismuth dodecanethiolate, crystalline bismuth nanoparticles are synthesized in a solvent-free environment at room temperature (24 ± 4 °C). Bi NPs are tested for catalytic activity by reducing 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with an excess of NaBH4. Dodecanethiol-capped bismuth nanoparticles exhibit an efficient reduction of 4-NP to 4-AP within 12 min. Additionally, these nanoparticles remain catalytically active for up to three cycles.