We investigated the effect of arbuscular mycorrhizal colonization (AMC) on ammonium-N uptake in the symbiotic system of marigold (Tagetes patula L.) and Glomus etunicatum (Becker and Gerd). Marigolds were cultivated in pots with five treatments at different P and N application levels with or without AMC. After growing the plants for 29 d, ^<15>N-ammonium-N was applied to each treatment. Twenty-four hours after ^<15>N-ammonium-N feeding, the plants were sampled for analysis. To evaluate the ammonium-N uptake activity of plant root, we determined the specific absorption rate of ammonium-N (SAR-AN : gN kg^<-1> root dry weight d^<-1>). The results obtained were summarized as follows : 1) At low P and N application levels, AMC increased the plant P concentration and decreased the plant N concentration. 2) The SAR-AN of marigold declined with the increase in plant P concentration due to AMC. The SAR-AN also declined with the increase in plant dry weight. However, the SAR-AN increased with the increase in plant N concentration. 3) The ^<15>N translocation from root to shoot was depressed due to AMC.