The structure of highly swollen micelles of an amphiphilic poly(oxyethylene)-poly(oxybutylene) diblock copolymer with a lengthy hydrophilic poly(oxyethylene) block has been investigated by small-angle neutron scattering (SANS). The density profile of the tethered polymer brush is obtained by fitting the SANS data using analytical expressions for the form factor of a micelle with a spherical core and self-avoiding chains. The decrease in coronal chain radius of gyration with increasing temperature, and the decrease in water content in the poly(oxybutylene) core lead to an increase in association number, in good agreement with previous light scattering experiments. The increase in polymer volume fraction close to the core on increasing temperature is related to the increase in fractional surface coverage and reduction in interfacial curvature.