The present invention relates to a method of producing a functional polymer particle having at least one kind of functional group selected from the following structure group (A), which comprises the step of reacting a non-crosslinked polymer particle having a succinimidoxycarbonyl group with a compound having at least one kind of functional group selected from the following structure group (A) and at least one functional group selected from the group consisting of a primary amino group and a secondary amino group: ##STR1##