Alfalfa (Medicago sativa L.) is one of the most important forage legumes worldwide and its productivity is limited by aluminum (Al) toxicity in acid soils. Single nucleotide polymorphisms (SNP) are the most abundant type of sequence differences between alleles and these may have functional relevance. Quantitative trait loci (QTL) for Al-tolerance were identified in a mapping population resulting from a cross between Altet-4 (Al tolerant) and NECS-141 (Al sensitive) using microsatellite markers.  The objectives of this study were to identify candidate genes responsible for Al-tolerance in tetraploid alfalfa and to develop SNP markers targeting these genes. A BLAST search of Al tolerance candidate genes was used to identify SNPs in alfalfa transcriptome sequences between Altet-4 and NECS-141 in relevant genes. High resolution melting (HRM) analysis was used for SNP genotyping in segregating populations.  Candidate genes were positioned in the linkage map and their co-segregation with Al tolerance QTL was evaluated.  Ongoing work involves evaluating differential gene expression of candidate gene targets.  Identification of gene(s) relevant to Al tolerance in alfalfa can facilitate the implementation of molecular breeding strategies and biotechnology approaches to develop alfalfa cultivars that are productive in acid and Al toxic soils.