Biphasic processes are used in whole-cell biotransformation to overcome the low water solubility of substrates and products as well as their inhibitory effects on the biocatalyst. Commercially available [NTf(2)]- and [PF(6)]-based ionic liquids (ILs) were used in a biphasic system for the 15α-hydroxylation of 13-ethyl-gon-4-en-3,17-dione by Penicillium raistrickii. With the substrate at 5 g l(-1) and a volume ratio of IL to buffer, buffer pH and cell density at, 1:9, 6.5, 16.8 g(DW) l(-1), respectively, the 15α-hydroxylation of 13-ethyl-gon-4-en-3,17-dione was achieved with a yield of 70 % after 72 h using [BMIm][NTf(2)] in a 50 ml biphasic system. This is compared to a 30 % yield in a monophasic aqueous system. This suggests the potential industrial application of ILs-based biphasic systems for steroid biotransformation.