Abstract: Using laser scanning confocal microscopy, we tested the mechanism of mitogen-activated protein kinase (MAPK) regulation of salicylic acid (SA)- or abscisic acid (ABA)-induced reactive oxygen species H2O2 elevation in Vicia guard cells. SB202190, a special inhibitor of p38 MAPK, blocked the elevation of H2O2 by SA but not ABA, whereas SB202190 alone could not increase H2O2 or Ca2+ level in guard cells. The combination of BAPTA, the chelator of Ca2+, and SA+SB202190 could not increase H2O2 level, which suggests that activation of p38 MAPK-like especially modulates H2O2 signaling in plant cells, regardless of Ca2+ level, similar to the mechanism in mammalian or yeast cells. To our knowledge, this is the first report that SB202190 regulates SAinduced ROS signaling in plant cells.