Abstract: Taking Eucalyptus urophylla and E. grandis × urophylla, as test materials, 2 mycorrhizal trials were conducted in 1993 and 1994 at Zhenhai Forest Farm, Kaiping of Guangdong Province. A split plot design was employed with 4 replicates, 2 host species, 8 ectomycorrhizal fungi and 6 or 9 trees per plot(experiment 1), or 3 ectomycorrhizal fungi and 9 trees per plot(experiment 2). After planting, tree height(H), diameter at ground level(D) and diameter at breast height(DBH) were measured at regular intervals. Effectiveness of isolates inoculated for E. grandis × urophylla were significantly different in all indexes between fungus treatments, by analysis of variation(ANOVA) for single species of data per experiment, the effectiveness of isolates for Eucalyptus urophylla were only significantly different in a few indexes between fungus treatments when using the same isolates as E. grandis × urophylla, which meant that tree genotype affected the effectiveness of ectomycorrhizal fungi in field; By ANOVA for 2 host species of data per experiment, order of variation composition for all indexes in experiment 1 was genotype effect genotype × fungus interaction effect or fungus effect, the order for tree height in experiment 2 was genotype effect genotype × fungus interaction effect or fungus effect, the order for DBH in experiment 2 was fungus effect genotype effect genotype × fungus interaction effect; In experiment 1, only D at 3 months after planting was significantly different between genotype × fungus interaction; In experiment 2, only tree heights at 6 months after planting was significantly different between the interaction. Finally, the role of tree genotype in applying ectomycorrhizal fungi was discussed.