The nucleotide sequences of the cylindrical inclusion protein (CIP) genes of two Japanese zucchini yellow mosaic virus (ZYMV) isolates (ZYMV-169 and ZYMV-M) were determined. The CIP genes of both isolates comprised 1902 nucleotides and encoded 634 amino acids containing consensus nucleotide binding motif. The sequence similarities between the two isolates at the nucleotide and amino acid levels were 91% and 98%, respectively. When the CIP gene sequences of the Japanese ZYMV isolates were compared with those of previously reported ZYMV isolates, the nucleotide and amino acid sequence similarities ranged between 81% and 97%, and between 95% and 97%, respectively. Phylogenetic analysis of the deduced amino acid sequences of the CIP genes indicated that the Japanese ZYMV isolates were closely related to those of other ZYMV isolates.