Technical Abstract: Straighthead is a physiological disorder in rice resulting in sterile florets, poorly developed panicles, and yield loss. Because of its sporadic nature and unidentified causes for the disorder, molecular marker assisted selection is essential for resistance improvement in breeding programs. To take advantage of recent advances in gene-mapping technology, we executed a genome-wide association mapping to identify genetic markers associated with straighthead disorder using 547 accessions of germplasm from the USDA rice core collection. Straighthead was evaluated in arsenic treated soil and genotyping was conducted with 75 molecular markers covering the entire rice genome about every 35 cM. A mixed-linear model approach combining the principal component assignments with kinship estimates proved to be particularly promising for association mapping. The extent of linkage disequilibrium was described among the markers. Six markers were found to be highly and significantly associated with straighthead, explaining ~35% of the total phenotypic variation. However, only two SSR markers, RM413 and RM277 on chromosome 5 and 12, respectively have a significant association with low rating indicating straighthead resistance. Confirmation with segregating populations, i.e., F2 or recombinant inbred lines, is necessary before marker-assisted selection can be applied.