This article presents the distribution of the local void fraction (alpha) in a mock-up bisectional bubble column with a diameter of 0.63 m. Owing to the lack of such data in the literature, alpha was investigated experimentally using a microresistivity (R) probe and a phase discrimination procedure based on the probe signal. The two-phase mixture that consisted of air and tap water was measured at 342 nodes in the vertical half-section plane of the column. Relatively small differences between the volume-integrated local values of alpha and the measured total gas holdups showed reasonably good agreement under all conditions. Experimental data were used for validation of a bubble column numerical model for a low hydrodynamic regime with commercial computational fluid dynamics (CFD) code. The difference between the CFD calculated total gas holdup and the experimentally measured mean value is 8.8%, while some differences in the local void fraction distributions were found in the lower part of the column. (c) 2019 American Institute of Chemical Engineers AIChE J, 65: 1186-1197, 2019