Strain A6 of leptospire was isolated from blood culture of a case with leptospirosis on July 1, 1962 in Mengla county, Xishuangbanna, Yunnan. It is proved a new serovar belonging to serogroup Autumnalis by cross agglutination and cross agglutinin-absorption tests. The name, Leprospira interrogans serovar nanla with reference strain A6 is proposed.