It has been well established that gamma rays at low doses have stimulatory effects on plant growth and development. However, our knowledge regarding the molecular mechanism underlying the growth stimulation remains limited. In this study, we report the role of reactive oxygen species (ROS) and abscisic acid (ABA) in the growth stimulation using irradiated Arabidopsis seeds. The results indicated that 50 Gy gamma irradiation presented maximal beneficial effects on germination index, root length, and fresh weight. The contents of hydrogen peroxide (H2O2) and activities of antioxidant enzymes under gamma irradiation were markedly higher than those of controls. ROS scavenging significantly suppressed the growth of the irradiated plants. Furthermore, endogenous ABA was induced under low-dose gamma irradiation. The growth stimulation and elevated H2O2 level were affected in the irradiated ABA-deficient mutant aba2-1 compared with the mutant control. Transcriptional expression analysis of selected genes revealed that several genes for ABA biosynthesis were upregulated, and the genes for ABA catabolic pathway and transport were differentially regulated in response to low-dose gamma irradiation. Our results suggest that ROS and ABA signaling play an essential role in the stimulatory effects of low-dose gamma irradiation and that ROS, as secondary molecules, mediate ABA signal transduction under irradiation in response to stress factors during plant growth.