Mastitis is an inflammatory response of the mammary gland to irritation, injury, or infectious agents and is a major problem in the dairy industry. We genotyped bovine major histocompatibility complex (BoLA)-DRB3 and BoLA-DQA1 genes in 120 Holstein cattle with clinical mastitis and 85 randomly selected Holstein cattle in Japan by polymerase chain reaction-sequence-based typing. The mastitis cattle were divided into four groups according to the bacterial species that caused the mastitis (Staphylococcus aureus, Streptococci, Escherichia, and coagulase-negative staphylococci). The BoLA-DRB3 and BoLA-DQA1 heterozygosity of each group was compared with that of the control cattle, while the expected heterozygosities based on Hardy-Weinberg proportions and the observed heterozygosities for each locus were compared for each group. The Escherichia-induced and Streptococci-induced mastitis groups showed significant differences between their expected and observed heterozygosities with regard to their BoLA-DQA1 genes. No differences were observed for any group with regard to the BoLA-DRB3 genes. We then found that two BoLA-DQA1 alleles promoted susceptibility to Streptococci-induced mastitis, namely BoLA-DQA1*0101 and BoLA-DQA1*10012 and that the homozygous BoLA-DQA1*0101/0101 and BoLA-DQA1*10011/10011 genotypes promoted susceptibility to mastitis caused by Streptococci and Escherichia, respectively. This is the first report showing that heterozygosity of the BoLA-DQA1 gene is associated with resistance to mastitis progression.