Studies on the determination of Critical Micelle Concentration (CMC), of mixed surfactants were carried out at 30°C for hexadecyltrimethylammonium bromide (HTAB) and polyoxyethylene sorbitan monolaurate (Tween 20)/1-Hexanol/water. The phase diagram, CMC value and the ideality of mixed surfactant were determined and the result indicated a composition of 0.2 to 1.0 fraction of water is the best area for normal micelle region for HTAB and 0.3 to 1.0 fraction of water for Tween 20 with curving upward the 1-hexanol apex maximum solubility of 1-hexanol. From the fluorescence method, the CMC value for pure T20 is 1.6293 x10^-3 M. While for CMC₁ and CMC₂ value for pure HTAB is CMC₁:5.4877 x10^-3 M and CMC₂:1.0975 x10^-2 M. Then, CMC value for mixed surfactant system at mole ratio 0.2: 0.8 (T20: HTAB) is 2.358 x10^-3 M.