In this study, the polarization effect in III-nitride based ultraviolet (UV) light-emitting diodes (LEDs) has been investigated theoretically. Some specific designs in active region are proposed to reduce the polarization effect and, hence, improve the device performance. Simulation results show that by utilizing properly designed quaternary AlInGaN material in active region, the hole injection efficiency can be enhanced due to the reduction of polarization mismatch between hetero-layers. On the other hand, the electron leakage is suppressed owing to that the effective potential height for electrons is increased. Therefore, the performance of UV LEDs is significantly improved by the polarization engineering in active region.