The ornithine decarboxylase (ODC) gene is a candidate gene for growth and carcass traits. It is located on chicken chromosome 3 in a region where QTL for growth and carcass traits have previously been detected in the F₂ population. The objectives of this study were to identify polymorphisms of the ODC gene in an F₂ resource population and to examine the effects of these ODC polymorphisms on growth and carcass traits. The F₂ resource population was obtained by crossing a Shamo male and White Plymouth Rock females. The F₂ population was then measured for growth and carcass traits and used for positional candidate gene analysis. A total of 6 novel SNP and a novel indel mutation were identified in the parental population. Three SNP (g.-638A>G, g.-465C>T, and g.-353C>T) and a 4-bp indel mutation (g.-633_-632ins) in the promoter region of the ODC gene were identified in the parental population, and 2 haplotypes composed of these mutations were segregated in the parental population. A QTL analysis was performed, and the QTL for some growth and carcass traits were detected at a significant level and on a similar position to the ODC gene. Significant associations were found between haplotypes in the promoter region of the ODC gene and these traits in the F₂ population, and the effect of haplotype on BW at 9 wk of age was the most significant. The haplotypes of the ODC gene found in this study might help in understanding the genetic structure of growth and carcass traits and in improving these traits directly by MAS. Therefore, further functional studies are necessary to evaluate the effects of promoter mutations at a molecular level.