Coexistence curves of (T-n) (T and n are temperature and refractive index, respectively) for {N,N-dimethylaccetamide(DMA)/sodiumbis(2-ethylhexyl)sulfosuccinate(AOT)/n-octane} nonaqueousmicroemulsion systems with various molar ratios ωs of DMA to AOT have been determined by the measurement of refractive index. Critical exponents (β) and critical amplitudes (B) were deduced fromcoexistence curves of (T-n). Results show that the critical volume fraction φc {i.e. φ=(VAOT+VDMA)/(VAOT+VDMA+Vn-octane)} increases as ωs decreases, but the critical temperature Tc increases with the increase in ωs. Value of the critical exponent βis independent of ωs and approaches 0.365, which is consistentwith the Fisher-renormalization group theory. System-dependence amplitudes (B) increase almost linearly with the increase in ωs.