Abstract: Provided is a method for modulating RNA splicing by inducing a base mutation at a splice site or a base substitution in a polypyrimidine region. The method comprises expressing a targeting cytosine deaminase in a cell, to induce AG at a 3? splice site of an intron of interest in a gene of interest to mutate into AA, or to induce GT at a 5? splice site of the intron of interest in a gene of interest to mutate to AT, or to induce a plurality of Cs in a polypyrimidine region of the intron of interest in a gene of interest to respectively mutate into Ts. The method specifically blocks an exon recognition process, modulates a selective splicing process of endogenous mRNA, induces exon skipping, activates an alternative splice site, induces mutually exclusive exon conversion, induces intron retention, and enhances an exon.