Monodisperse, thermosensitive microspheres with sub-micron diameters are used for separation and collection of proteins and other biomolecules. The thermosensitivity gives the microspheres two valuable features. One is the controllability of affinity between microsphere and protein with temperature. The quality and quantity of proteins to be adsorbed on the microspheres can be controlled with temperature. The other feature is reversible control of dispersion stability. Microspheres which have adsorbed target proteins in the dispersion can be easily recovered by changing temperature.