A late hydrothermal lens have been found by the authors in the serpenti- mite at Guanyuan-Bao arer, Asbestos County Sichuan Province. In the lens two types of regulaly interstratified septechlorite-swelling chlorite (Se-Cg) and chlorite-antigorite (C-An) have been identified. Both the Se-Cg and the C-An have a evident sharp reflection at about 32A in the X-ray diffraction patterns. Behaviours and position of the d(001), d(002) reflection of both the regularly interstratifies minerals at 300 ℃，400℃，540℃，600℃ and 700℃ were analyzed and discussed in this paper. Properties of associated minerals; leuchtanbergite and septechlorite were reported in this paper, too.