Transcriptome of barley Hordeum vulgare grown aboard International Space Station (ISS) was analyzed by means of microarray. It was revealed 500 genes with mRNA level, changed more than two folds in space environment. Among them are genes encoding stress response proteins, videlicet Heat Shock Proteins (HSP), Pathogenesis-Related Proteins (PR) and Antioxidant Proteins. Further analysis of these genes by real time PCR showed enhanced transcription level of Reactive oxygen Species (ROS) scavenging genes. The mRNA level of superoxide dismutase (sod) was 6 folds higher in space environment when compare to Earth conditions. Glutamyl transferase gene expression was enhanced 24 times in space. Transcription of catalase gene (cat) was increased 18 times and of ascorbate peroxidase was increased 3 times in space in comparison with ground control. For the first time it was shown that space flight environment may induce oxidative stress in plants.