Nutrient availability and interspecific competition may affect emergent wetland plant growth and resource allocation in constructed wetland. A glasshouse study was conducted to investigate the influence of nutrient and mixture between Canna indica Linn and Schoenoplectus validus (Vahl) A. Love & D. Love on their growth and resource allocation in the wetland microcosms, using simulated secondary-treated municipal wastewater effluent with either low (17.5 mg N and 10 mg P 1(-1)) or high (35 mg N and 20 mg P 1(-1)) nutrient concentrations. After 65 days, the high nutrient treatment stimulated plant growth and resulted in allocation of more resources to the above-ground tissues compared to below-ground ones. The concentrations of N and P in the plant tissues (except P in above-ground tissues) were significantly higher, whereas N and P use efficiencies were significantly lower in the high than the low nutrient treatment. The total biomass for C. indica in mixture increased significantly in the high nutrient treatment, but that for S. validus was significantly lower in mixture than in monoculture. Relative yield (RY) indicated that there was significant interspecific competition between S. validus and C. indica in mixtures, with C. indica being the superior competitor. The growth of S. validus was significantly inhibited by the presence of C. indica in their mixture. Compared with monoculture, S. validus in mixture had significantly higher percentages of root biomass and allocations of N and P to roots, whereas C. indica was not significantly affected by mixture. The results suggested that the growth and resource allocation of C. indica and S. validus could be altered by nutrient availability and interspecific competition in constructed wetlands.