A pot experiment was conducted to reveal the effects of an arbuscular mycorrhizal fungus, Glomus mosseae, on carbon (C)∶nitrogen (N)∶phosphorus (P) ratios and RNA contents of clover plants at different N and P addition levels. The experimental results indicated that Glomus mosseae colonization increased the biomass, P concentrations and C/N ratios, while decreased N concentrations, C/P and N/P ratios, under P addition level of or lower than 50 mg kg-1. Under P addition level of 100 mg kg-1, Glomus mosseae colonization showed no significant effects on the biomass, nutrient concentrations and C∶N∶P ratios of clover plants. Generally Glomus mosseae colonization increased RNA contents of clover plants compared with non-mycorrhizal controls. For non-mycorrhizal clover, P concentrations were positively correlated with RNA contents, indicating the changes in P concentrations can alter RNA contents of clover plants. C concentrations were significantly related to N, P concentrations in clover plants, suggesting that the changes in C concentrations depended on N and P concentrations. Furthermore, N/P ratios of clover plants were also mediated by N/P supply ratios in soil.