The applicability of an online sample preconcentration technique, large volume sample stacking with electroosmotic flow pump (LVSEP), to microchip zone electrophoresis (MCZE) for the analysis of oligosaccharides was investigated. Since the sample stacking and separation proceeded successively without polarity switching in LVSEP, a single 'straight' channel microchip could be employed. To suppress the sample adsorption onto the channel surface in the MCZE analysis of oligosaccharides, the straight microchannel was modified with poly(vinyl alcohol) (PVA). Although it is well-known that the PVA coating can suppress the electroosmotic flow (EOF), an enhanced EOF occurred temporarily in a low ionic strength sample solution, which worked as the driving force to remove the sample matrix in LVSEP. To evaluate the analytical performance of LVSEP-MCZE, oligosaccharides were analyzed in the PVA-coated straight channel. As a result, both glucose ladder and oligosaccharides released from bovine ribonuclease B were well enriched and separated with up to a 2900-fold sensitivity enhancement compared with a conventional MCZE analysis. By applying the LVSEP technique to MCZE, a voltage program for fluidic control could be simplified from four channels for two steps to two channels for one step.