The gene of buckwheat trypsin inhibitor (BTI) has been cloned and expressed in Escherichia coli. The yield of this recombinant inhibitor was over 12 mg/L by using one-step purification on a Ni2+-NTA Sepharose column. Its molecular weight was 9322.1 Da, determined by mass spectrum analysis. The MTT and cytometry analyses showed that recombinant BTI could specifically inhibit the proliferation of IM-9 human B lymphoblastoid cells (from patient with multiple myeloma) in a dose-dependent manner. The test of recombinant BTI-induced apoptosis in IM-9 cells implied that the inhibitor might have potential application in the treatment of cancer.