Tinan ludwigite, a new Sn-rich subspecies of ludwigite, occurs in a magnesian skarn borate deposit at Qiliping, Changning County, Hunan province. The SnO_2 content of the mineral varies from 4.6 to 12.0 wt. %, and the chemical formula is (Mg(1.64)Fe_(0.35)(2+)Mn(0.01)(2.00)(Fe(0.55)(3+)Sn(0.16)Mg(0.28))(0.99)BO5, which has never been previously reported. The authors have studied the mineral in such aspects as its optical and physical properties, chemical composition, X-ray crystallography, and crystallochemistry, with a crystallographic comparison given between this mineral and its analogues.From the above investigation, the authors have come to the conclusion that Fe(3+) position has been occupied by Sn(4+) in the crystal structure and the charge is compensated by having Mg(2+) It is also the authors' opinion that tin not only is a minor component but also serves as a species-forming element ludwigite.