Iodine sorption of polyacrylonitrile(PAN) in aqueous I$_2$/KI solution was investigated for structural study of PAN. The sorption behaviors for uniaxially oriented film and unoriented film show a distinct difference below the concentration of O.8mole/l. The dimension of oriented film treated above this concentration recovers its original dimension. As the diffusion of iodine into PAN is the mode of non-Fickian, the diffusion coefficient increases with time of sorption. The sorption behavior in disordered region of oriented film is found to be similar to that of unoriented film. It is ascertained that iodine is able to penetrate into ordered as well as disordered region of PAN below the concentration of 0.5 mole/l.