The critical behavior of a cationic surfactant, butyl-tetradecyldimethylammonium bromide, in an aqueous 4M-NaBr solution was investigated concerning the isothermal osmotic compressibility and long-range correlation length by means of light scattering, coexistence curve, and turbidity. The critical exponents were obtained as gamma’=1.39+/-0.04 and nu’=0.70+/-0.03 together with xi(0)= (2.48+/-0.06) nm, and beta’ = 0.375+/-0.01. The temperature dependence of turbidity showed a good accordance with the result of light scattering measurement. Negative alpha’ was obtained from the scaling relation. The critical exponents are in good agreement with the Fisher-renormalization prediction for the ternary system (almost fully renormalized Ising exponents).