The present invention relates to an antibody binding to Claudin6 (CLDN6) expressed on a cell membrane. The antibody of the present invention recognizes human CLDN6 present in a native form on cell membrane surface and exhibits cytotoxicity through ADCC and/or CDC activities against cancer cell lines highly expressing human CLDN6. Moreover, the antibody of the present invention has cell growth inhibitory effect through conjugation with toxin on cancer cell lines highly expressing human CLDN6. The human CLDN6 is overexpressed in tumor tissues (lung adenocarcinoma, gastric cancer, and ovarian cancer), although its expression is not observed in normal tissues. Thus, the anti-CLDN6 antibody is expected to highly accumulate in tumors highly expressing human CLDN6 and can serve as a very effective antitumor agent.
