The behaviors of improved Heat transfer and the associated higher pressure drop for liquid flow in rectangular micochannels with longitudinal vortex generators (LVGs) were determined experimentally for the Reynolds numbers of 170-1200 with hydraulic diameter of 187.5 mu m and aspect ratio of 0.067 for LVGs with different number of pairs and angles of attack. It was found that the range of critical Reynolds numbers (600-730) were at a much smaller value by adding LVGs than the one without (Re similar to 2300): heat transfer performance was improved (9-21% higher for those with laminar flow and 39-90% for those with turbulent flow), while encountering larger pressure drop (34-83% for laminar flow and 61-169% for turbulent flow). Empirical correlations for these two parameters were then obtained by curve-fittings for a variety of rectangular microchannels under study. (C) 2011 Elsevier Ltd. All rights reserved.