To provide an anti-human MUC1 antibody Fab fragment, which is expected to be useful for the diagnosis and/or treatment of cancer, particularly the diagnosis and/or treatment of breast cancer or bladder cancer, and a diagnosis means and/or a therapeutic means using a complex containing the Fab fragment. An anti-human MUC1 antibody Fab fragment which contains a heavy chain fragment containing a heavy-chain variable region comprising the amino acid sequence represented by SEQ ID NO: 8 or 10, and a light chain containing a light-chain variable region comprising the amino acid sequence represented by SEQ ID NO: 12； and a complex containing the Fab fragment.本發明提供一種期待對於診斷及/或治療，特別對於乳癌或膀胱癌之診斷及/或治療上為有用之使用含有抗人類MUC1抗體Fab片段，及該Fab片段的複合體之診斷手段及/或治療手段。 本發明的解決手段為，具有含有由序列號碼8或10所示胺基酸序列所成的重鏈可變區域之重鏈片段，及含有由序列號碼12所示胺基酸序列所成的輕鏈可變區域之輕鏈的含有抗人類MUC1抗體Fab片段，及該Fab片段之複合體。
