OBJECTIVE: DNA methylation has been regarded as an important genetics marker reflecting the transcription state of DNA in cells. This study aimed to assess the methylation of CpG island in 5' promotor region of p15 and p16 genes in children with hepatoblastoma, and to explore its relationship with the development of hepatoblastoma. METHODS: The methylation-specific polymerase chain reaction (MSP) and PCR-SSCP techniques were used to analyze DNA methylation. The tumor tissues, the tissues beside the tumor and normal tissues beyond the tumor in 30 cases with hepatoblastoma were studied by nested MSP. The target fragment was verified by gel electrophoresis and sequencing. RESULTS: The incidence of abnormal methylation of 5' CpG island of p15 and p16 genes in tumor tissues was 30% (9/30) and 67% (20/30) respectively. It was 20% (6/30) and 57% (17/30) respectively in the tissues beside tumor and that was 13% (4/30) and 33% (10/30) respectively in the normal tissues beyond the tumor. Homozygous deletion of exon 2 of p15 gene was found in 1 of 30 cases (3%) in hepatoblastoma. No deletion of exon 1 or intron 1 was found. Heterozygosis deletion of exon 2 of p16 gene and partial intron 2 was found in 3 of 30 cases (10%). No deletion of exon 1 or intron 1 was found. CONCLUSIONS: The abnormal methylation of CpG island in 5' promotor region of p15 and p16 genes appears to play a role in the development of hepatoblastoma, which might be attributed to the inhibition of gene transcription by abnormal methyaltion of CpG island in the promotor region.