The purpose of this work was to study the effect of a new high porosity packing (solid fraction corresponds to 0.5%) on the hydrodynamics of two bubble columns of different diameters (15 and 20 cm) operating with co-current up-flow of gas and liquid. This specific packing is a stainless steel welded grid with a mesh size of 12.5 mm. Two types of gas sparger were used. Gas hold up, gas hold up profiles bubble size, slip velocity and liquid axial dispersion coefficients were determined with and without packing. The results obtained show that this type of packing has a considerable effect: it delays regime transition and can maintain a homogeneous regime over a large range of superficial gas velocities. Liquid axial mixing was also greatly affected by the presence of this packing, tending toward plug flow.