1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid ([BMIM]+[BF4]-) was synthesized using N-methylimidazole and 1-bromobutane as starting materials by two-step method. The obtained ionic liquid was characterized by IR spectra. Gold nanochains were prepared through the reduction of HAuCl4 by NaBH4 in [BMIM]+[BF4]-. UV-Vis spectra and TEM images reveal that the prepared nano gold is mainly chain-like. The ionic liquid not only acts as reaction medium but also as modifier in the preparation of nano gold.