Using the VOF multiphase flow model, numerical simulations are conducted to investigate the nucleate boiling of water in micro-channels. The Marangoni heat transfer through the bubble surface is analyzed, and is compared with the incipient heat flux at the onset of nucleate boiling in micro-channels. The bubble growth in the channel is divided into two stages. At the initial stage, bubble growth is controlled by surface tension, while at the second stage the incipient heat transfer dominated the boiling process. In the results, the full process of bubble generating, growing, departing, combining, and shrinking in the channel is displayed. The simulated results with similar condition are agreed well with some experimental results in references. The method and discussion in the paper are helpful to the investigation of the mechanism of micro-scale two-phase flow and heat transfer. (C) 2009 Elsevier Ltd. All rights reserved.