Abstract: The extraction of the thallus of Porphyra haitanensis by phosphate buffer was precipitated with (MH₄)₂SO₄, purified further by DEAE-Sepharose column and Sephadex G-100 column . The purified lectin (PHL) could bind monosaccharides (Ara, Gal and Xyl) and maltose to which PHL had the strongest binding. In cell agglutinations, PHL agglutinated erythrocytes from rabbit, sheep and chicken, but not from duck, pigeon and human A, B or O blood cell groups. Furthermore, PHL agglutinated marine microalga, Pavlova viridis, and fresh microalga, Chlorella pyrenoidosa. These agglutinations were related to algal cell density. The result that Bacillus subtilis and Saccharomycs cerevisiae in different conditions responsed to PHL differently indicated that lectin receptors on cell changed in different conditions.