The tick Boophilus microplus is one of the major ectoparasites that affect livestock, and conventional tick control has been based mainly on the use of acaricides. Therefore, efforts are being made to develop alternative approaches to tick control such as vaccines. It was showed that an aspartic protease purified from B. microplus eggs, named Boophilus Yolk pro-Cathepsin (BYC), confers a partial protection in experimental infestation with B. microplus. Here, we verified the immunoprotector effect of a recombinant BYC (rBYC) expressed in E. coli. Eight bovines from a naturally tick-free area were divided in two groups (control: animals 1, 2, 3, 4 and treatment: animals 5, 6, 7, 8). Treated group received 5 inoculations of purified rBYC (1st/2nd 50μg; 3rd 100μg; 4th/5th 200μg) in adjuvant Montanide at 10 days intervals. Controls received emulsion PBS/Montanide only. Ten days after the last inoculation bovines were challenged with 20,000 B. microplus larvae. After 16 days, ticks were collected and analyzed for the number of fully engorged females, egg viability, and posture capacity. Additionally, messenger RNA transcripts of interleukin (IL)-2, IL-4, IL-10 and interferon gamma (IFN-γ) were assayed by RT-PCR. Antibody titers were determinated in the day calves were challenged. Two animals presented a titer of 4,000, and the others a lower titer (500 and 1,000). The overall efficacy ratio against B. microplus was 25.24 %. Considering just the high antibody titer group, protection rate was of 40.53 %. Expression of IFN-γ occurred in all bovines. IL-10 expretion was observed in bovines 1, 2, 4, 5, 6 and 7, while IL 2 was detected only in bovines 2 and 6. The protection degree observed here are similar to the degree achieved using the native protein (Da Silva Vaz et al., 1998). Our results demonstrate that recombinant BYC kept immunoprotetive capacity and it varies according to antibody title.