Dynamic behavior of the drops and bubbles in developed turbulent flow depend on turbulent length scale (gimel), Morton (Mo), Weber (We) and Reynolds (Re-a) numbers. In the present work, in order to calculate the maximum stable size of drops and bubbles, the A factor of break-up, Ay (Ay = omegaa/U), that is the ratio of the break-up rate in developed turbulent flow to the mean velocity of the flow has been introduced and the effect of the pipe roughness on this factor has also been given. Comparison of all the results obtained in this study with those taken from the literature for the range of Mo less than or equal to 7, We less than or equal to 10 and Re-u less than or equal to 100 showed a good agreement. (C) 2004 Elsevier Ltd. All rights reserved.