The ternary critical mixture of 1,4-dioxane (1) + water (2) + saturated KCl (3) has a lower critical point. The density rho and refractive index n of this system have been measured as function of temperature for nine critical mixtures along the coexistence curve below the temperature of phase-transition. The water mole fraction in free basis x(2) in the mixtures extends from (0.550 to 0.880) and the molality m of KCl from 0.47 to 2.039 mol kg(-1). With increase of temperature, water mole fraction and KCl molality, the obtained density decreased, while the refractive index decreases with increase in temperature, water mole fraction and molality of salt. Both represented anomalies near the critical temperature T-C. The molar fraction of critical mixture, increase less than 1%, with temperature and decrease by 10%, with water mass fraction and molality of salt. The critical density and the critical refractive index vary linearly with water mass fraction w(2) with molality In of KCl as a third degree polynomial. The temperature of separation of phase T-t varies with critical composition in water and molality of KCl. (C) 2010 Elsevier B.V. All rights reserved.