Liver involvement in multiple myeloma has been known to be common in autopsied series. However, since its clinical significance is uncertain yet, invasive procedure confirming plasma cell infiltration of the liver has been rarely performed. We report a case with multiple myeloma which had plasma cell infiltration of a liver. A peritoneoscopic biopsy of the liver for the purpose of disclosing the nature of the aggravating liver function in a carrier of the hepatitis B virus showed infiltration of lymphoreticular cell which were identified later as lambda-light chain producing primitive plasma cells by immunohistochemical stain.