Abstract: An investigation on the fauna and ecology of small mammals on the Cangshan Mountain and Erhai Lake natural reserve was carried out from 1992 to 1995,and more than 1600 specimens belonged to 35 species were collected in the survey.Until now,53 species which belong to 30 genera,12 families and 5 orders,has been found in the reserve together with those recorded previously.According to the investigation in eight main ecological enviroments,the species diversity index is the highest in the coniferous and broadleaf mixed forest and lowest in the cultivated area while the highest density of small mammals is in the cultivated area and the lowest in the alpine bush or meadow.Among 33 species of small mammals in the vertical distribution investigation on both eastern and western slopes of Cangshan Mountain,21 species (63.63%)belong to Oriental realm and 10 species (30.30%)to Palaearctic realm,and 2 species (6.06%) to wide spread species.The elevation of 3100 m (in coniferous and broadleaf mixde forest) was the dividing line tetween the two regions in Cangshan Mountain.