Abstract: In this study, we propose a microstrip Ultra-Wideband (UWB) Bandstop Filter (BSF) using Dual Interdigital Capacitor Frequency Selective Coupling Structure (DIDC-FSCS). The proposed UWB BSF is designed based on lossless FSCS with transverse wave form. The designed BSF used two λ/4 lengths to make an interdigital capacitor and then make it dual FSCS. And one Shunt Open Circuit Resonator (SOCR) with an additional λ/4 length. The SOCR is composed of meander lines. The input and output ports were terminated to 50 Ω for the system application. The designed BSF was simulated using the Sonnet simulator. The measured center frequency is 6.3 GHz, the BSF 3 dB bandwidth is 4.2 GHz and the maximum transmission coefficient and the reflection coefficient are 35.0 and 0.43 dB, respectively. The actual size of the BSF is 10.0×12.57 mm.