Seasonal bioaccumulation of heavy metals namely, Zinc (Zn), Iron (Fe), Copper (Cu), Lead (Pb), Mercury (Hg) and Arsenic (As) in the shellfish of Macrobrachium rosenbergi from Niger River at Onitsha were studied using Atomic Absorption Spectrophotometer (AAS). Results showed presence of all the analysed metals in the shellfish tissue. Mean concentrations of Zn (4.35±1.2 mg/l), Cu (1.35±0.43), Cd (0.31±0.0421), Hg (0.16±0.0011) and As (0.04±0.001) in mg/l complied with the World Health Organization (WHO) standards in aquatic foods. However those for Fe (9.73±1.30) and Pb (0.24±0.04) mg/l exceeded the WHO standards. Furthermore, mean concentrations for Zn (0.321±0.09), Fe (1.52±0.07), Cu (0.035±0.006), Hg (0.076±0.007), As (0.016±0.007) and Cd (0.012±0.006) mg/l in the water columns were significantly lower (P<0.05) than the concentrations in the shellfish. Bioaccumulation of heavy metals in the shellfish studied indicated that Niger River at Onitsha is experiencing impairment. The result implies that prolonged consumption of shellfish and other aquatic foods contaminated with heavy metals, and through observed indiscriminate dumping of waste in the river, may constitute public health risks.