The photocopolymerizations of methyl methacrylate (M₁) with viny1 benzoate (M₂), using benzoy1 peroxide(BPO), benzoin(BN), and benzoin methyl ether(BME) as initiators, were carried out with UV irradiation at 30℃ to obtain transparent plastic rods. The copolymerization started and propagated gradually during the irradiation from the UV lamp-side inner wall of the glass tube, and the initial photocopolymerization rate increased with the increase of the monmer feed ratio (M₁/M₂) and/or the initiator concentration. During the polymerization of the MMA-VB mixture in glass tube, the polymerization temperatures varied with the sorts of initiators such as BPO, BN, and BME, and these temperatures should be attributed only to the heat of polymerization. Meanwhile, the maximum temperatures on the Temp, vs. time curves were well consistent with the inflection points of the corresponding conversion curves, respectictively By determining the monomer reactivity ratio and also observing the results which could be obtained from the copolymer composition and refractive-index distribution profiles along the sample thickness, We could conclude that MMA-VB copolymer may be applied to the graded index (GI type) optical fiber.