Severe diarrhea improved dramatically with administration of the humanized anti-interleukin-6 receptor antibody tocilizumab (TCZ) in a patient with secondary reactive amyloidosis, which was associated with rheumatoid arthritis (RA). A 53-year-old woman with RA went into hypovolemic shock because of severe watery diarrhea associated with gastrointestinal amyloidosis. The high-dose prednisolone therapy and glucocorticoid pulse therapy did not improve her intractable diarrhea. After TCZ administration, the life-threatening diarrhea lessened in about 6 h, and her vital signs became stable the next day. Perforation of the small intestine, however, occurred 2 days after TCZ administration. Whether TCZ could have been involved in the perforation in such a short time is unknown. Surgery was successful, and the patient recovered. TCZ may work immediately in diarrhea associated with secondary amyloidosis.