Total flavonoids contents in above- and under-ground parts of four fern plants including Pteris multifida Poir.,Dryopteris erythrosora ( Eaton) O. Ktze, D. championii ( Benth.) C. Chr. and Cyrtomium fortunei J. Smith from Zijin Mountain of Nanjing in April were determined and compared. The results show that total flavonoids contents in under-ground parts of four fern plants all are higher than that in above-ground part. In which, total flavonoids content in under-ground part of C. fortunei is the highest with a mass ratio of 2. 41% , that in above-ground part of D. championii is the highest with a mass ratio of 1. 05% , while that in above- and under-ground parts of P. multifida are the lowest with a mass ratio of 0. 31% and 0. 38% , respectively. Total flavonoids contents in under-ground parts of C. fortunei and D. erythrosora respectively are 2. 95 and 2. 77 times of their above-ground parts with an obvious difference, so their under-ground parts can be used as materials for extracting total flavonoids.