The present invention aims at establishing a molecular therapy for Alport syndrome. The present invention provides an oligonucleotide of 15-30 bp comprising a nucleotide sequence complementary to the cDNA of COL4A5 gene, wherein the oligonucleotide is capable of inducing skipping of an exon which has a truncating mutation found in COL4A5 gene in Alport syndrome patients and whose nucleotide number is a multiple of 3, a pharmaceutically acceptable salt thereof, or a solvate thereof. Also provided is a pharmaceutical drug comprising the above oligonucleotide, a pharmaceutically acceptable salt thereof, or a solvate thereof (therapeutic drug for Alport syndrome).