The bovine tick Rhipicephalus (Boophilus) microplus is a blood sucking animal responsible for Babesia spp and Anaplasma marginale transmission for cattle. Using recombinant DNA methods, a B. microplus fat body cDNA library was constructed using SMART System Kit. 465 clones were selected and sequenced randomly and resulted in 60 contigs. Among them we were able to identify an Open Reading Frame (ORF) with 98 amino acids, which was named Bmcystatin, because of 70% amino acid identity to a classical type 1 cystatin from Ixodes scapularis tick (GenBank accession AAM93646). The Bmcystatin amino acid sequence analysis showed two cysteine residues, theoretical pI of 5.92 and Mr of 11 kDa. Bmcystatin gene was cloned in pET 26b vector and the protein expressed in bacteria Escherichia coli BL21 SI. Bmcystatin purified by affinity chromatography on Ni-NTA agarose column and ionic exchange chromatography on Hitrap Q column presented molecular mass of 11 kDa, by SDS-PAGE and the N-terminal amino acid sequenced revealed unprocessed N-terminal containing part of pelB signal sequence. The recombinant Bmcystatin showed to be a C1 cysteine peptidases inhibitor with Ki value of  0.1 nM and 0.6 nM for human cathepsin L and VTDCE (Vitellin Degrading Cysteine Endopeptidase), respectively. The Bmcystatin expression was analyzed by semi-quantitative RT-PCR amplifying a DNA sequence (298 bp) only in the fat body cDNA preparation. On the other hand, the protein was detected in the fat body and the salivary gland extracts using anti-Bmcystatin antibody by Western blot. The perspectives of this work will be the immunolocalization of Bmcystatin in different tissues of B. microplus and also look for its physiological function by RNA interference. Financial Supported by FAPESP, Pronex-FAPERJ and CNPq.