Aberrant sialylation and altered sialyltransferase (ST) expressions are frequently found in many types of cancer. In this study, we examined the expressions of α 2,3-linked sialic acid residues and STs mRNA in human gastric cancer tissues. The relationship between the levels of α 2,3-linked sialic acid residues and the expression of STs mRNA was also analyzed. Maackia amurensis leukoagglutinin (MAL) specific for α 2,3-linked sialic acid was used for immunohistochemical staining. All gastric cancer tissues were positive for MAL staining, whereas adjacent normal tissues were negative. The extent of MAL staining was significantly correlated with the behavior of gastric cancer. The expression of STs mRNA was examined by real-time quantitative reverse transcription-polymerase chain reaction assay. The levels of ST3Gal IV and ST6GalI in gastric cancer tissues were significantly increased compared with those in adjacent normal tissues (P < 0.05), whereas the levels of ST3Gal I, ST3Gal III, and ST3Gal VI were not increased. Furthermore, the high expression of ST3Gal IV was closely related to the extent of MAL staining (P < 0.05) unlike that of ST6Gal I. These results indicated that gastric cancer tissues expressed high levels of α 2,3-linked sialic acid residues, ST3Gal IV, and ST6Gal I. The high expression of ST3Gal IV may contribute to the expression of α 2,3-linked sialic acid residues, which is associated with the malignant behavior of gastric cancer cells.