In the present work, a 4-point optical probe (Xue, J., Al-Dahhan, M., Dudukovic, M.P., Mudde, R.E, 2008a. AlChE J. 54, 350-363) was applied to a slurry bubble column to assess the effect of solids on bubble dynamics. All experiments were performed in an 8 in, diameter column operated in the churn turbulent regime. Air and water were used as gas and liquid mediums respectively, and the slurry consisted of either 10% [by weight] aluminum oxide catalyst particles with 60 mu pm average diameter or glass spheres in the 0.3 mm-0.35 mm size range. Local gas hold-up and bubble frequency were reduced in the presence of both solids. However, bubble velocity increased in the presence of aluminum oxide catalyst particles, and is slightly reduced in presence of glass spheres, compared to a system with no solids. The volumetric mass transfer coefficient was lower in the presence of aluminum oxide catalyst particles, and a slight reduction in the gas-liquid interfacial area was observed., (C) 2015 Elsevier Ltd. All rights reserved.