The experimental and numerical research on microchannel heat transfer and fluid flow was presented in the paper. Diameters of the microtubes were 0.1, 0.3 and 0.5 mm and the flow regime was laminar with Re-number range up to 800. The working fluid was distilled water and the tube material was stainless steel. The experimental setup was designed in such a way that the investigation of the average friction factor and developing heat transfer was possible. Due to the large scattering in the reported experimental results, the scope of this research was to make the accurate measurements and to compare the experimental heat transfer and fluid flow characteristics with numerical and theoretical results for the conventional tubes. (C) 2004 Elsevier Ltd. All rights reserved.