Excess molar volumes of an aqueous solution of non-ionic surfactant n-hexyl pentaoxyethene glycol monoether {CH3(CH2)(5)O(CH2CH2O)(5)H} (C6E5) have been investigated as a function of composition and temperature. The measurements in the vicinity of the critical micelle composition (c.m.c.) have been made at the temperatures (288.146, 298.144, and 308.141) K. The excess molar volume V-m(E) is negative and increases with temperature. V-m(E)(x) changes slope at x = (0.0015, 0.0020, and 0.0024) at the temperatures (288.146, 298.144, and 308.141) K, respectively. The results for V-m(E) have been fitted to an association model and the values of the aggregation number N, Delta V-m,V-micell, and critical micelle composition have been extracted.