The selective oxidation of cyclopentene to maleic anhydride (MA) and phthalic anhydride (PA) has been studied using V-P(vanadium-phosphorus) oxide catalysts supported by TiO2(anatase). In the catalysts with 3.5 wt% V-P loading, V-P active components were effectively dispersed on a low surface area of TiO2(anatase) forming thin layers. The catalysts with appropriate P/V ratios were effective in the selective oxidation of cyclopentene. As the content of P (phosphorus) in the active component of the catalysts was increased, the oxidation activity was decreased, but the selectivity of MA was increased to a maximum at the P/V atomic ratio of 0.5 before decrease. For P/V atomic ratios of 0∼1.1, however, the selectivity of PA was gradually increased. A maximum value determined by the sum of the selectivities of MA and PA, was obtained at the P/V atomic ratio of 0.7 and ca.(????) 50%. On the other hand, the increased loading of active components in the P/V atomic ratio of 0.7 resulted in minor decreases of the oxidation activity and the selectivity of the desired products, MA and PA. In addition, the effects due to P/V atomic ratios were discussed in connection with the reaction mechanism for the selective oxidation of cyclopentene.