Abstract: In the extraction systems of Penicillin G model with aqueous solutions of cetyltrimetyl ammonium bromide (CTAB) as aqueous phase and butyl acetate as organic phase, third phase was found at certain conditions. The third was phase formed at the concentration of CTAB lower 0.054 mol/L and at the fixed concentration of Pencillin G 0.042mol/L. The surface tension and viscosity was affected little by increasing the concentration change of CTAB and Pencillin G. Conductivity was affected by increasing the concentration change of CTAB. It was proven that the water and BA were dissloved each other in the third phase. By the component analysis method, the concentration ratio of CTAB and Pencillin G was 1. The third phase was lamellar structure by the observation of transmission electronic microscope (TEM).