A large bubble rising in a narrow fixed bed is visualized by the index matching method, which makes particles and cylinder invisible by matching the refractive index between the material and the liquid. The bubble velocity is nearly independent of size in the narrow bed while it decreases with size in the pipe. The velocity in the bed sensitively increases with a superficial liquid velocity while a notable dependency is not observed in the pipe. The bubble behavior is modeled by a VOF (volume of fluid) method associated with a high-fidelity CFD (computational fluid dynamics) model, which can treat hundreds of particles that are randomly packed in the bed without geometrical simplification. The CFD model is validated based on the comparison between experimental and numerical results.