A greenhouse study was conducted to determine the influence of soil compaction on root growth of yellow poplar (Liriodendrontulipifera L.) and sweet gum (Liquidambarstyraciflua L.) seedlings grown in association with the mycorrhizal fungi Glomusmacrocarpum Tul. and Tul. or G. fasciculatum (Thaxt) Gerd. and Trappe. Seedlings were transplanted into pots that contained silt loam compacted to bulk densities of 1.25, 1.40, or 1.55 Mg m−3. Fungal chlamydospores or control filtrates were used to inoculate seedlings. Weight and length of yellow poplar roots were significantly greater at the lower bulk densities than at the highest bulk density, but fibrosity of the root system was unaffected by increasing bulk density. Weight, length, and fibrosity of the sweetgum root system decreased significantly with each increase in bulk density. Inoculated yellow poplar seedlings had greater root weight at each bulk density than noninoculated seedlings, but root length was not influenced by mycorrhizal treatments at higher bulk densities. Fibrosity of yellow poplar roots varied by mycorrhizal treatment at each bulk density. Results indicate that for yellow poplar, compaction effects may outweigh mycorrhizal benefits at higher bulk densities. At each bulk density, sweet gum seedlings inoculated with G. fasciculatum showed the greatest root growth, suggesting that effects of compaction can be alleviated for sweet gum by inoculation with this mycorrhizal fungus.