A proficiency testing (PT) program for the determination of aflatoxin M1 (AFM1) in milk powder was designed and conducted so as to identify the interlaboratory differences and to understand, assess and improve the proficiency of the participant laboratories. Split-level test samples were prepared according to the Guidance on Statistical Treatment of Proficiency Testing Results and Proficiency Evaluation (CNAS?CL002), and the uniformity and stability of the samples were analyzed by one-way analysis of variance and t test, respectively. Robust statistical analysis of the proficiency testing results was conducted to evaluate laboratory proficiency through Z score. The homogeneity and stability of the samples met the requirements of proficiency testing. Of 49 laboratories that reported results for AFM1 in milk powder, 45 (91.8%) performed satisfactorily. The majority of the participant laboratories passed the proficiency testing with satisfactory results, indicating that the laboratory performance for the determination of AFM1 in milk powder was generally good. The outlier results found in a few laboratories was largely ascribed to experimental operation and data processing errors.