HLA-A66 (A66) is a human leukocyte antigen serotype within HLA-A serotype group.

The serotype is determined by the antibody recognition of α66 subset of HLA-A α-chains.

For A66, the alpha "A" chain are encoded by the HLA-A*66 allele group and the β-chain are encoded by B2M locus.

A66 is more common in Africa and Southwest Europe.

A66 (A*6601) is believed to have been formed by a single gene conversion between another HLA-A and the A*2601 allele.[2].