PURPOSE: To prepare a carrier having increased capability to support biological substances, by treating an organic particle with a silanecoupling agent and/or a titanium coupling agent.

CONSTITUTION: A particle having organic surface, e.g. a polymer particle is treated with a silane-coupling agent such as the compound of formula I [X is halogen, OR, or OC(O)R (R is 1W3C alkyl); R' is alkyl, alkenyl or allyl] and/or a titanium coupling agent such as the compound of formula II (R" is alkoxy or carboxy; R''' is alkylcarboxy, substituted benzenesulfoxy, substituted phenoxy, etc.; m is 1W3) to obtain the objective carrier. The treatment can be carried out e.g. by adding the coupling agent directly or in the form of a water-miscible organic solvent solution to the aqueous dispersion of the organic particles.