The present work tried to determine the effects of the three polyamine (PA) species (100 mg L-1), putrescine (Put), spermidine (Spd) and spermine (Spm), on root colox`nization, root morphology and phosphorus (P) uptake of three-month-old citrus (Citrus tangerine) seedlings inoculated with arbuscular mycorrhizal fungus (AMF), Glomus mosseae. Exogenous PAs significantly increased root colonization three months after application. Sole AMF inoculation notably improved root morphology (total length, total projected area, total surface area and total volume) and growth performance (plant height, stem diameter and leaf number per plant) in comparison with non-mycorrhizal control, whilst PAs application to mycorrhizal seedlings increased more these root morphological and growth traits. AMF significantly reduced guaiacol peroxidase (G-POD) activity of root, whereas G-POD activities of mycorrhizal leaf and root were elevated by Pas, to a certain extent. Compared with sole AMF treatment, exogenous PAs significantly inhibited acid and neutral phosphatase activities of rhizosphere. Moreover, exogenous PAs notably reduced available P content of rhizosphere but significantly increased root P content. It concluded that exogenous PAs could stimulate both root colonization and morphology, and root morphological improvement of mycorrhizal seedlings by PAs was related to not G-POD activity but to root P level and would result in an increment of growth performance.