Aldehyde dehydrogenase (ALDH) superfamily represents a group of NAD(P)(+)-dependent enzymes that catalyze the oxidation of endogenous and exogenous aldehydes to the corresponding carboxylic acids. A total of twenty ALDH genes were identified in the rice genome. They were grouped into 10 distinct families based on protein sequence identity. The whole genome duplication (WGD) predating the divergence of cereals and tandem duplications represent the major mechanism for this superfamily expansion. Intron loss was found to accompany the recent evolution of four rice ALDH families. Quantitative RT-PCR analysis revealed that some of the rice ALDH genes were expressed in an organ-specific manner. Microarray data analysis indicated that expression of most duplicated rice ALDH genes showed high tissue specificities. Diverse expression patterns for duplicated genes were evaluated using both microarray and MPSS data. Expression levels of some ALDH genes were up-regulated by drought and high salinity stresses and the phytohormone abscisic acid (ABA) application, indicating that the products of these genes were potentially involved in rice osmotic stress adaptation. These results suggested that the specific rice ALDH genes might be potentially useful in rice genetic improvement.