ADP-ribosylation factor (ARF) family proteins, one type of small guanine-nucleotide-binding (G) proteins, play a central role in regulating vesicular traffic and organelle structures in eukaryotes. The Arabidopsis (Arabidopsis thaliana) genome contains more than 21 ARF proteins, but relatively little is known about the functional heterogeneity of ARF homologs in plants. Here, we characterized the function of a unique ARF protein, ARFD1B, in Arabidopsis. ARFD1B exhibited both cytosol and punctate localization patterns, colocalizing with a Golgi marker in protoplasts and transgenic plants. Distinct from other ARF1 homologs, overexpression of a dominant-negative mutant form of ARFD1B did not alter the localization of the Golgi marker mannosidase I (ManI)-RFP in Arabidopsis cells. Interestingly, the ARFD1 artificial microRNA knockdown mutant arfd1 displayed a deleterious growth phenotype, while this phenotype was restored in complemented plants. Further, confocal imaging and transmission electron microscopy analyses of the arfd1 mutant revealed defective cell plate formation and abnormal Golgi morphology. Pull-down and liquid chromatography-tandem mass spectrometry analyses identified Coat Protein I (COPI) components as interacting partners of ARFD1B, and subsequent bimolecular fluorescence complementation, yeast (Saccharomyces cerevisiae) two-hybrid, and co-immunoprecipitation assays further confirmed these interactions. These results demonstrate that ARFD1 is required for cell plate formation, maintenance of Golgi morphology, and plant growth in Arabidopsis.