Deficient in DNA Methylation 1 (DDM1) protein is required to maintain the DNA methylation status of Arabidopsis thaliana. DDM1 is a member of the broad SWI2/SNF2 protein family. Because of its phylogenetic position, DDM1 has been speculated to act as a chromatin-remodeling factor. Here we used a purified recombinant DDM1 protein to investigate whether it can remodel chromatin in vitro. We show that DDM1 is an ATPase stimulated by both naked and nucleosomal DNA. DDM1 binds to the nucleosome and promotes chromatin remodeling in an ATP-dependent manner. Specifically, it induces nucleosome repositioning on a short DNA fragment. The enzymatic activity of DDM1 is not affected by DNA methylation. The relevance of these findings to the in vivorole of DDM1 is discussed.