Objective To test the stability of serum samples in proficiency tests. Methods In accordance with CNAS-CL04(CNAS: China National Accreditation Service for Conformity Assessment), serum samples of inbred mice were tested for storage stability, acceleration stability, transport stability, and final stability. Results The samples were stable at -20℃ or 4℃ for 50 days. The samples were stable at 37℃ or room temperature for 27 days. The samples were stable during transportation. All samples passed the final stability test. Conclusions The collected serum samples met the requirements for proficiency tests. Serum samples of esterase-1 were adequate for proficiency testing.