The photocopolymerization of methyl methacrylate(MMA) with vinyl benzoate(VB), using benzoyl peroxide(BPO) as an initiator, was carried out with UV irradiation to obtain a transparent GRIN rod. The resulting GRIN rod has a parabolic gradient of refractive index in the region near the center axis(radius Rc), and index-distribution constant A and the normalized radius Rc were measured by the reduction rate of an image and the view field of the rod lens. An increase in monomer feed ratio, MMA/VB(wt/wt) ranging from 2.5 to 5.0 results in the increase of A but the decrease of Rc. The value of A grew very high at BPO=1.0wt% and MMA/VB=4.0, and the value of Rc monotonically decreased with the BPO concentration. Elevation of the polymerization temperature caused the decrease in both A and Rc. The index distribution from the center to the periphery showed a similar shape, regardless to the sample compositions. The GRIN rod shows convex lens characteristics which are necessary properties in use of imaging and light-focusing devices.