We report the high fidelity on-chip fractionation of selected segrnents, from an electrophoretic flow of separated fragments. dsDNA fragments (10- 330 base pairs were initially separated using a 6.5 cm long channel with an electric field strength of 150 V/cm. As an example of the fractionation process, a target fragment of 20 bp was selected and extracted from the separation channel. The extraction was confirmed and evaluated by fluorescence imaging. High resolution and extraction fidelity were achieved by introducing new. procedures or (i) extraction channel-blocking and (ii) segment transfer with cleaning. These procedures are necessary for the development of a practical, fully automated multitarget fractionation electrophoretic chip. A kind of itCb image processing method was introduced to monitor, control, and evaluate the procedure of fractionation. The resolution limits of the separation and extraction are discussed.