In 2004, PGL-1 Test was applied for people who had close contacts with leprosy patients in Khanh Hoa. People having PGL-1 (+) without skin lesion got single dose of ROM and were followed from 2004-2009. Among people getting preventive chemotherapy, none of them was detected to have leprosy. New detected leprosy cases during 2005-2009 are 84 patients, considerably decreasing compared to the number before using preventive chemotherapy. Among people having PGL -1 (-), 2 of them contracted leoprosy after 1 year and 2 years. Therefore, the application of PGL-1 test for early detection of Mycobacterium lepea infection without symptoms and using ROM regimen as a preventive chemotherapy have been proved effective for leprosy prevention program in Khanh Hoa province, contributed to the reduction of dectection rate to 0.86/100,000 population in 2009.