Abstract: The present invention relates to a cytosine base-editing composition, and more specifically, to a cytosine base-editing composition comprising adenine deaminase and CRISPR-associated protein 9 (Cas9), or functional analogs thereof, which has a narrow editing window and thus is capable of accurately editing cytosine in a target sequence with another base. The present inventors have discovered that the application of the cytosine base-editing composition comprising adenine deaminase and Cas9, or functional analogs thereof, to a target sequence, causes cytosine on a specific motif to be substituted with another base, and that existing adenine base editors (ABEs) are capable of editing not only adenine but also cytosine, and can also have said substitutions occur with higher accuracy compared to existing cytosine base editors (CBEs).