AtRAN1 belongs to RAN GTPase family in Arabidopsis thaliana.In our study, we found AtRAN1 have a relatively specific expression in gametophytes, embryos and endosperm at reproductive growth stage of Arabidopsis.The AtRAN1 knock-down homozygote had smaller flowers and yielded smaller seeds than WT.In mature AtRAN1 knock-down mutant embryo, cell size instead of cell number was significantly reduced compared with WT, indicating AtRAN1 may take part in seed development.