To provide agents for skipping of the 53rd exon of a human dystrophin gene with high efficiency.SOLUTION : The present invention provides an oligonucleotide enabling skipping of the 53rd exon of a human dystrophin gene, or an antisense oligomer in which the sugar moiety and/or phosphoric acid binding moiety of at least one nucleotide constituting the oligonucleotide is modified, and a pharmaceutical composition for treating muscular dystrophy containing the antisense oligomer and a pharmaceutically acceptable salt or hydrate thereof as active ingredients.SELECTED DRAWING : None