A method for the production of a microsphere without use of a dispersion stabilizer is disclosed which permits the microsphere to be produced in the form of discrete particles readily treatable for purification. The method which produces this microsphere comprises the steps of dissolving in an organic solvent such as an alcohol a monomer mixture including an ethylenically unsaturated amide and 10 to 70% by weight, based on 100% by weight of said monomer mixture, of a cross-linking agent thereby preparing a mixed solution, keeping said mixed solution at a temperature in the range of from 30.degree. to 95.degree. C., and adding thereto at least one initiator selected from the group consisting of peroxide type initiators and azo type initiators in an amount such as to be contained therein at a final concentration in the range of from 1.times.10.sup.-5 to 8.times.10.sup.-2 mol/liter thereby inducing polymerization of said monomer mixture. The microsphere consequently obtained can be used as one kind of a substrate most suitable for the preparation of an affinity adsorbent serving ideally as a filler for use in affinity chromatography.