The aggregation behaviors of branched block polyether Tetronic 1107 (T1107) at an air/liquid surface was investigated in mixed solvents consisting of water and one of the following polar cosolvents: ethanol, n-propanol, ethylene glycol (EG), or glycerol (GLY). Surface tension measurements provide information about the effects of cosolvents on the critical micellization concentration (cmc), the standard Gibbs energy (Delta G(mic)degrees), the maximum surface excess concentration (Gamma(max)), the minimum area per polyether molecule at the air/liquid surface (A(min)), and the standard free energy of adsorption (Delta G(ads)degrees,). The addition of ethanol and n-propanol to water disfavors the micellization and progressively increases the cmc of T1107, whereas the cmc decreases with the addition of EG and GLY. The values of Delta G(mic)degrees of T1107 are all negative in mixed solvents, and their absolute values become smaller as the ethanol or n-propanol content increases but become larger as the EG or GLY content increases. The cosolvents have a significant effect on the surface adsorption and cmc, and the order is as follows: n-propanol water > ethanol water > water > EG water > GLY water. The octanol/water partition coefficient (log P) of the cosolvent is used to correlate the effects, and it could capture the effect of cosolvents on the cmc qualitatively. The surface dilational theological properties of T1107 in water and water alcohol mixtures were also studied by surface dilational viscoelasticity and surface tension relaxation measurements. The dilational elasticity decreases monotonously in the presence of ethanol or n-propanol. With the increasing concentration of EG and GLY, the dilational elasticity of T1107 passes through a maximum that coincides with the change in Gamma(max).