A novel graded index (GI) plastic rod was prepared by interfacial-gel polymerization carried out in a poly(methyl methacrylate) (PMMA) tube with one closed end. Bromobenzene (BE) was used to obtain a graded index distribution and neodymium octanate (NOA) as a dye with Nd3+ concentrations from 60 to 700 ppm. For a polymerization system containing methyl methacrylate (MMA) as monomers, azobis-isobutyronitrile (AIBN) as an initiator, and dodecyl mercaptain as chain transfer agents, the difference of the refractive index from the center to the periphery of the rod (Delta n) was found to be 0.015 at 18 wt % of BE and 60 ppm of Nd3+. Experimental results also showed that a parabolic profile of refractive index formed on the cross section of the rod and Delta n increased with BB contents increasing. NOA has little effect on the profile within the given concentrations. A description for forming the GI distribution is given by the free volume theory.