This study was conducted to assess the reliability of Nerita lineata as a bioindicator for metals in sediment and the factors influencing the accumulation of metals and methylmercury in its soft tissue. The two matrices were analyzed for Co, Cr, Cu, THg, MeHg, Mn, Ni, Pb, and Zn. The metal concentrations in N. lineata were comparable to previously reported results with the exception of Ni which was higher. Cu, Mn, and Pb in N. lineata were significantly (p < 0.05) positively correlated with the respective elements in the sediment, while the biota-sediment accumulation factor showed that Cu, THg, MeHg, and Ni were bioconcentrated in N. lineata. This suggests that N. lineata has the potential to be a bioindicator for Cu, THg, MeHg, Mn, Ni, and Pb. The results also suggest an indirect relationship between THg in the sediment and the MeHg concentration in N. lineata in which periphyton might play a role. The affinity of Cr, Cu, Pb, and Zn with Mn (oxides) in sediment was also found to be a factor influencing their accumulation in N. lineata.