The study was conducted for evaluating the efficacy of Circovac vaccine in preventing diseases caused by Porcine Circovirus type 2 (PCV) in pigs of Thanh Long company, Luong Son, Hoa Binh. The experiments were carried out in two trials. In each trial, there were 10 sows divided into 2 groups with and without vaccination. The results showed that Circovac vaccinated sows had better titers of antibodies against PCV2 \han the unvaccinated sows. The percentage of PCV2 antibody positive samples collected from vaccination group were 100 percent with or = 3log2 titer, whereas only 9/20 (45 percent) samples collected from nonvaccination group had PCV2 antibody with low titer (3log2). Comparison with the control group, using Circovac had shown to be highly efficacious in terms of reduced mortality, number of culls, and improved growth performance (p0.05).