Abstract: Methylmercury concentrations of inflows and outflows in cascade reservoirs in Wujiang River were determined by distillation-ethylation (GC-CVAFS) technique in 2006. The distribution and temporal and spatial variation of methylmercury were discussed. The results were as follows: ρ(total methylmercury) ranged from 0.07 to 0.70 ng/L and ρ(dissolved methylmercury) from 0.03 to 0.16 ng/L in inflows. In outflows ρ(total methylmercury) ranged from 0.10 to 0.34 ng/L and ρ(dissolved methylmercury) from 0.04 to 0.26 ng/L. The obvious positive relationship between ρ(total methylmercury) and ρ(total suspended matter) was found in inflows, and ρ(total methylmercury) in high flow was higher than that in low flow. ρ(total methylmercury) in outflows collected in summer and fall were significantly higher than those sampled in winter and spring. The ρ(methylmercury) increased at several sites below reservoir because of the construction of cascade reservoirs, therefore, it is possible that ρ(methylmercury) would increase dramatically with the development of reservoir.