Liquid-liquid (L-L), solidliquid (S-L), and solid-liquid-liquid (S-L-L) equilibrium data for the water-ethanol-1-undecanol ternary system have been determined experimentally at (275.15, 278.15, 281.15, 288.15, and 298.15) K and atmospheric pressure. Different shapes of the equilibrium diagrams have been observed depending on the temperature. A region with three phases (S-L-L) is present in the temperature range between (275.15 and 281.15) K. Above 288.15 K, only a L-L region is observed.