Abstract: In order to understand more comprehensively and objectively the ability of various analytical laboratories in Shanghai on determination of residual amounts of sulfonamides (SAs) in aquatic products, and to give more scientific comments on this subject, a program of inter-laboratory proficiency test on this item was proposed and carried out. 17 labs signed up voluntarily to join the test. Positive samples of fish were obtained by drug-breeding. Homogeneity and stability of the samples were tested by the single factor variance analysis and the significance test. Analytical results reported by the participated labs were treated by the robust statistics and assessed by the Z-scores. 15 of the 17 labs gave satisfactory results; and as a whole, the analytical capacity of these labs for the testing item was recognized to be satisfactory. Furthermore, upon analysis of the results reported, it was realized that the methods used for sample pretreatment and use of SRMs were key links for introducing errors.