Detergent is critical for membrane protein purification, impacting the state of oligomerization, crystallization conditions and other physicochemical properties. Analytical ultracentrifugation (AUC), by characterizing the sedimentation of membrane protein-detergent complex in centrifugal fields, is able to measure various hydrodynamic and thermodynamic properties, including sedimentation coefficient, molar mass, hydrodynamic radius, binding coefficient, thus defining the homogeneity and oligomerization state of membrane protein-detergent complex. This study focuses on an ABC transporter from thermophilic bacteria, TmrAB, and utilizes AUC coupled to size-exclusion chromatography and negative staining electron microscopy to determine its homogeneity, oligomerization, and stoichiometry of membrane protein and detergent molecules. The results indicate that TmrAB complex exists as homogeneous monomer of heterodimers of TmrA and TmrB, in the condition of 8× Critical Micelle Concentration (CMC) DDM, having a ratio of DDM/TmrAB equal to 116∶1. This study suggests, AUC is a reliable method to analyze the molecular mass of membrane protein.