To identify genes related to plant mitochondrial morphology and dynamics, novel mutants with respect to mitochondrial morphology were isolated from an ethyl methane sulphonate (EMS)-mutated population of Arabidopsis thaliana. Mitochondria were visualized by transforming Arabidopsis with a gene for a fusion protein consisting of GFP and a mitochondria-targeting pre-sequence. From 19,000 M2 populations, 17 mutants were isolated by fluorescent microscopic observations. All mitochondria in these mutants were longer and/or larger than wild-type mitochondria. The approximate chromosomal loci of the mutations of seven mutants that grew well were determined. The mitochondrial phenotypes of six of the mutants were recessive but the mitochondrial phenotype of the seventh mutant was dominant. Chromosomal rough mapping of the seven mutants showed that the mutations occurred at four different loci. At least one of these loci was novel, i.e., it was different from loci of other known mitochondrial morphology mutants of Arabidopsis and different from loci of Arabidopsis homologues of yeast genes related to mitochondrial morphology.