Fifty-five serum samples from patients with leptospirosis treated by the method of high SiO2 concentration salt solution absorption were analysed with the variable sequences of the 16S rRNA genes of Leptospria interrogans as primers. It is shown that the 16S rRNA gene primer is useful for the clinical detection and the epidemic investigation of leptospirosis, and the detecting effect by PCR is superior to that by the blood culture and MAT (P < 0.01).