The study was carried out in a two-chambered rootbox separated by 37-μm nylon mesh to establish root+hyphae chamber carrying trifoliate orange (Poncirus trifoliata) as the test plant inoculated with Diversispora versiformis and hyphae chamber (without roots). This objective is to evaluate whether exogenous phytohormones regulate mycorrhizal effects on root hairs. Indole butyric acid (IBA), abscisic acid (ABA), and jasmonic acid (JA) (each at 0.1 μM concentration) were weekly applied into hyphae chamber, in total of six times before plant harvest. Mycorrhization strongly stimulated plant growth performance, and exogenous phytohormones, especially IBA, further magnified the mycorrhizal-stimulated growth response. Three exogenous phytohormones significantly decreased mycorrhizal colonization in taproot and first-order lateral roots, but increased in second-and third-order lateral roots, compared with non-phytohormone treatment in mycorrhozal plants. These phytohormones also increased hyphal length in nylon mesh and soil, irrespective of root+hyphae or hyphae chamber. Mycorrhizal inoculation significantly increased root hair density in different root classes, and exogenous hormones further strengthened the mycorrhizal effect. Average root hair length was stimulated by mycorrhization, but all exogenous phytohormones weakened the mycorrhizal response. Mycorrhization in combination with exogenous phytohormones showed no response on root hair diameter. Hence, the result suggested that application of exogenous phytohormones in hyphae chamber strengthened the D. versiformis-induced change in root hair density but weakened in root hair length in trifoliate orange grown in root+hyphae chamber.