A biodegradable flocculant or bioflocculant was prepared from hen egg white protein. Egg albumin was ethyl-esterified in a 0.1 M HCl ethyl alcohol solution at room temperature. Ethyl-esterified egg albumin (EtOA), having an esterification degree of 84%, was applied to the flocculation of diatomite. The flocculating ability of EtOA was evaluated by a clarification test and the sedimentation balance method. The diatomite suspension was effectively flocculated by the addition of small amount of EtOA (1 wt% of the diatomite weight), and the flocculating ability of EtOA was higher than that of poly aluminum chloride at pH 4 to 10. The settling velocity of diatomite floc at the appropriate MeCS dosage (1-2 wt%) was about 0.005 m.s(-1) at pH <7, and it decreased to 0.003 m.s(-1) at pH >7.