Arabidopsis thaliana belongs to those plants that do not naturally accumulate glycine betaine (GB), although its genome contains two genes, ALDH10A8 and ALDH10A9 that code for betaine aldehyde dehydrogenases (BADHs). BADHs were initially known to catalyze the last step of the biosynthesis of GB in plants. But they can also oxidize metabolism-derived aminoaldehydes to their corresponding amino acids in some cases. This study was carried out to investigate the functional properties of Arabidopsis BADH genes. Here, we have shown that ALDH10A8 and ALDH10A9 proteins are targeted to leucoplasts and peroxisomes, respectively. The expression patterns of ALDH10A8 and ALDH10A9 genes have been analysed under abiotic stress conditions. Both genes are expressed in the plant and weakly induced by ABA, salt, chilling (4°C), methyl viologen and dehydration. The role of the ALDH10A8 gene was analysed using T-DNA insertion mutants. There was no phenotypic difference between wild-type and mutant plants in the absence of stress. But ALDH10A8 seedlings and 4-week-old plants were more sensitive to dehydration and salt stress than wild-type plants. The recombinant ALDH10A9 enzyme was shown to oxidize betaine aldehyde, 4-aminobutyraldehyde and 3-aminopropionaldehyde to their corresponding carboxylic acids. We hypothesize that ALDH10A8 or ALDH10A9 may serve as detoxification enzymes controlling the level of aminoaldehydes, which are produced in cellular metabolism under stress conditions.