<p>Conformational and colloidal stabilities are responsible for the stability of hemoglobin. However, most hemoglobin _A1c (HbA_1c) control materials (e.g., reference materials, calibrators, and quality control materials) are unstable and noncommutable. This may be closely related to the breakdown of the balance between the conformational and colloidal stabilities of hemoglobin. Therefore, we developed a new combined formulation buffer to address the causes of conformational and colloidal instabilities and to maintain hemoglobin or HbA_1c stability. For the commutability of HbA_1c control materials, we purified hemoglobin to remove plasma proteins, phospholipids, and fats. On the basis of the above design, we prepared two medical concentrations of HbA_1c control materials for the external quality assessment (EQA) program and then determined the certified values via the reference measurement method. Stability, homogeneity, value transfer, and commutability were evaluated. Moreover, the control material was distributed to 56 laboratories to assess proficiency testing. The HbA_1c control materials showed good homogeneity and stability and reliable value transfer, and were commutable for routine clinical analyzers. In the EQA program, only one analyzer exceeded the acceptable bias range (± 6.0%), and the mean interlaboratory <i>CV</i>s of the three analyzers exceeded the acceptable range (3.0%), which can be used to assess true values to improve proficiency testing in the EQA program. Therefore, newly developed control materials can be used to standardize the determination of HbA_1c.</p> Graphical Abstract <p></p>