Objective To investigate the single nucleotide polymorphism(SNP) in the coding region in cytochrome P4501A1(CYP1A1) gene and to evaluate the contributions of SNPs to acute lymphocytic leukemia(ALL) and acute myeloid leukemia(AML) susceptibility in children. Methods One hundred and twenty-one(male 76, female 45) children with acute leukemia were selected from Department of Hematology in Shenzhen Children's Hospital, Zuyi Medical College between January 2007 and January 2014 as the case study group, and the average age was 4.42 years old.Case study group included 101 (male 65, female 36, average age 4.38 years old) ALL children (ALL group)and 20(male 11, female 9, average age 4.66 years old) AML children(AML group). A total of 116(male 74, female 42) children with respiratory tract infections on health examination during the same period were selected as the control group and the average age was 3.93 years old.SNPs in the coding region in CYP1A1 gene were detected by reverse transcriptional(RT)-PCR-denaturing gradient gel elelctrphoresis(DGGE) combined with direct sequencing in the case study group and the control group. Results Only one SNP, A4889G, was screened in the open reading frame(ORF) of CYP1A1 gene in Chinese Han children and the G allele frequency of CYP1A1 gene in the case group, ALL group, AML group and the control group were 31.4%, 32.2%, 27.5% and 38.8%.The CYP1A1 A4889G AG and AG+ GG genotype were linked with decreased risk of AML(OR=0.31, 95%CI: 0.11-0.87, P=0.02; OR=0.35, 95%CI: 0.14-0.93, P=0.03) especially in boys with AML(OR=0.12, 95%CI: 0.03-0.60, P=0.01; OR=0.16, 95%CI: 0.04-0.65, P=0.01), but the CYP1A1 A4889G polymorphism was not associated with the risk of ALL(P>0.05). The CYP1A1 A4889G allele frequency and the distribution of genotypes were significantly different from those reported in America, India, Korea, Brazil and Iran(all P<0.05). Conclusions CYP1A1 A4889G polymorphism may be not associated with susceptibility to ALL, but may decrease the risk of childhood AML especially in boys with AML.In addition, it may exhibit an ethnic difference. Key words: Cytochrome P4501A1; Acute leukemia; Single nucleotide polymorphism; Child