Emery-Dreifuss muscular dystrophy is an inherited muscular disorder clinically characterized by slowly progressive weakness affecting humero-peroneal muscles, early joint contractures, and cardiomyopathy with conduction block. The X-linked recessive form is caused by mutation in the EMD gene encoding an integral protein of the inner nuclear membrane, emerin. In this study, mutant mice lacking emerin were produced by insertion of a neomycin resistance gene into exon 6 of the coding gene. Tissues taken from mutant mice lacked emerin. The mutant mice displayed a normal growth rate indistinguishable from their littermates and were fertile. No marked muscle weakness or joint abnormalities were observed; however, rotarod test revealed altered motor coordination. Electrocardiography showed mild prolongation of atrioventricular conduction time in emerin-lacking male mice older than 40 weeks of age. Electron microscopic analysis of skeletal and cardiac muscles from emerin-lacking mice revealed small vacuoles, which mostly bordered the myonuclei. Our results suggest that emerin deficiency causes minimal motor and cardiac dysfunctions in mice with a structural fragility of myonuclei.