The present invention provides an anti-mouse .alpha.9 integrin antibody, an anti-human .alpha.9 integrin antibody, a hybridoma producing any of the antibodies, a method of producing any of the antibodies and the hybridoma, and a pharmaceutical composition comprising any of the antibodies. The anti-.alpha.9 integrin antibody of the present invention inhibits the .alpha.9 integrin function thereby to exhibit therapeutic effects on cancer, e.g., the growth and metastasis of a cancer cell, and an inflammatory disease, e.g., rheumatoid arthritis, osteoarthritis, hepatitis, bronchial asthma, fibrosis, diabetes, arteriosclerosis, multiple sclerosis, granuloma, an inflammatory bowel disease (ulcerative colitis and Crohn's disease), an autoimmune disease and the like.