Using heteronuclear NMR spectroscopy, we studied the solution structure and dynamics of bovine β-lactoglobulin A at pH 2.0 and 45 °C, where the protein exists as a monomeric native state. The monomeric NMR structure, comprising an eight-stranded continuous antiparallel β-barrel and one major α-helix, is similar to the X-ray dimeric structure obtained at pH 6.2, including βI-strand that forms the dimer interface and loop EF that serves as a lid of the interior hydrophobic hole. {1H}-15N NOE revealed that βF, βG, and βH strands buried under the major α-helix are rigid on a pico- to nanosecond time scale and also emphasized rapid fluctuations of loops and the N- and C-terminal regions.