POSS-NH3Cl is introduced to polylactic acid (PLLA) by blending and grafting separately to improve the properties of PLLA, especially the transparency. A series of star-shaped polylactic acid is synthesized using L-lactic acid (L-LA) and octa (γ-chloroammoniumpropyl) octasilsesquioxane (POSS-NH3Cl) in the presence of stannous (II) octanoate [Sn(Otc)2] catalyst, and the mechanism is studied. Meanwhile, a series of composite cross-linked films are prepared by casting. The structures of these dendritic polymers are characterized by Fourier transform infrared spectra (FTIR), which conforms the presence of the grafting reaction at the same time. Ultraviolet (UV)-visible light transmittance analyzer is used to analyze the transparency of the composite films. It is found that polyethylene glycol (PEG) has little relation to the transparency of the film while the content of POSS-NH3Cl affected the transparency. The grafted products exhibit superior transparent property than blend ones due to better compatibility with the PLLA. The transparency of the film improves even 40% in some wavelength, which is explained theoretically.