In this paper, a novel compact 3-D dual-mode stepped-impedance resonator (SIR) with centrally loaded stub is constructed for designing a wideband low-temperature cofired ceramic (LTCC) bandpass filter (BPF). By fully taking advantage of the LTCC technology, the dual-mode SIR, as a cell unit of the proposed filter, is reasonably folded in 3-D environment, and its properties are investigated using the transmission line theory. Accordingly, benefiting from the 3-D circuit layout, the proposed BPF designed by combining the SIR and dual-mode techniques can effectively overcome a vital and common drawback of large circuit size of the LTCC distributed-element filters. For demonstration, a fourth-order wideband BPF centered at 5 GHz is designed, fabricated, and measured. The circuit size of the designed BPF has a compact size of $3.875times 4.8times 1.4$ mm $^{3}$ . The impact of the package on the coupling and routing scheme and frequency response/transmission zero has been analyzed and demonstrated. The simulated and measured results are presented and compared, showing a good agreement.