PURPOSE: To separate effectively and efficiently microbial cells, by adding a cationic high polymer, particularly cationic modified starch as a flocculant to a microbial suspension in separating the microbial cells therefrom.

CONSTITUTION: Microbial cells are efficiently separated from a suspension thereof by adding a cationic high polymer, particularly a cationic modified starch as a flocculant thereto. A tertiary cationic modified starch obtained by reacting 2-diethylaminoethyl chloride, etc. with corn, tapioca, wheat starch or another starch, quaternary cationic modified starch obtained by reacting 2- chloroethyltrimethylammonium chloride therewith, tertiary and quaternary cationic graft modified starch obtained by graft copolymerizing dimethylaminoethyl acrylate, etc. therewith and combination thereof are preferred for the cationic high polymer.