A dinucleotide analogue which incorporates a 5-aza-cytosine as a base residue in the sequence of the dinucleotide analogue. The dinucleotide is linked with a phospholinker and has the general formula of: a. Z-L-G, or G-L-Z, wherein Z is 5-aza-cytosine； G is guanine and L is a phospholinker covalently linking Z and G； or b. 5'-DpG-3' or 5'GpD-3', wherein D is decitabine； p is a phospholinker； and G is deoxyguanosine. The dinucleotide can be used in a method for inhibiting DNA methylation or for treating diseases associated with aberrant DNA methylation.
