Excess molar volumes of an aqueous solution of a non-ionic surfactant : n-octyl tetraoxyethene glycol monoether, {CH3(CH2)(7)O(CH2CH2O)(4)H} ("C8E4") have been investigated as a function of temperature in the high dilute region, i.e. the region in the vicinity of the critical micelle composition (c.m.c.). The measurements have been made at the temperatures (278.149, 288.146, 298.144, and 308.141)K. In this study, V-m(E) is negative and increases with temperature; V-m(E)(x) changes slope for x = (0.00024, 0.00020, 0.00017, and 0.00013) at the temperatures (278.149, 288.146, 298.144, and 308.141)K, respectively. The results for V-m(E) have been fitted with an association model, and the values of the aggregation number N, Delta V-m,V-micell and the critical micelle composition have been extracted.