Abstract: The effect of anion microemulsion SDS/n-C₄H₉OH/n-C₇H₁₆H₂O as a medium on Ferric-Thiocyanate complexes is studied at 20℃. The results show that the maximum absorption wave λ_maxbalhochromic shift and the sensitivity is raised in comparison with water as a medium when the three kinds of microemulsions are used as the medium respectively such as O/W, W/O and transitional structure between them, hut the W/O microemulsion is the best medium. And the λ_maxba-thochromic shift 20nm and the sensitivity is enhanced about one time when the W/O microemulsion containing 20% water is used.