The interactions of the surface active ionic liquid (IL), 1-butyl-3-methylimidazolium octylsulfate [BMIM] [OS], with lysozyme were studied using tensiometry, turbidimetry, absorbance, fluorescence spectra, circular dichroism (CD), and Fourier transformed infra red (FTIR) techniques in phosphate buffer medium (pH 6 and 8) at 298 K. In the studied media coacervate was formed and the coacervation process depended on protein concentration. Isoemissive points were observed in emission spectra of lysozyme with IL. The isoemissive wavelength depended on the pH of the solution and also on [lysozyme]. The denaturation of lysozyme depended on the medium pH and the added [IL] as revealed from the CD and FTIR measurements. Molecular docking has provided information of the region of the lysozyme surface where the IL started to bind with it.