Employing soil core method, an investigation in Maoershan Experiment Station was made on the root biomass, specific root length (SRL), and root length density (RLD) of Fraxinus mandshurica plantation (17 yr) within a growth season in stand level. The results showed that the total root biomass was 1,637 g x m(-2), in which, living biomass accounted for 85%, and necrotic biomass was 15%. In the living biomass, coarse roots (5 approximately 30 mm in diameter) had the highest percentage (69.95 %), followed by fine roots (< 1 mm in diameter) (13.53 %), medium roots (2 approximately 5 mm in diameter) (7.21%), and small roots (1 approximately 2 mm in diameter) (9.31%). Among the four diameter classes, fine roots had a higher SRL (32.20 m x g(-1)), while coarse roots had a lower one (0.08 m x g(-1)). The total RLD in living biomass was 6,602.54 m x m(-2) in stand level, among which, fine root accounted for 92.43%, and the others was less than 8%. Fine root biomass and RLD had a positive correlation with soil available nitrogen, while no significant correlation was found between SRL and soil available nitrogen.