Human activities have contributed heavy metals to streams, wetlands and, eventually, coastal waters and sediments. Numerous studies have demonstrated that the total metal content in a wetland or sediments is a poor indicator to its bioavailability. Predicting bioavailability of heavy metals in wetlands and sediments is not simple, yet it is essential for environmental risk assessment and management decision in polluted waters. Recent studies have suggested that sulfur chemistry may hold the key to the understanding of heavy metal bioavailability in sediments. Report here are the results of our study based on this development. The objectives of this paper are 1) to review the control of sulfur chemistry on metal solubility (bioavailability) in sediments; 2) to present a proper expression of metal sulfide chemistry in sediments; and 3) to propose two chemical indicators for predicting heavy metal bioavailability in sediments. Metal sulfides are extremely insoluble (non-toxic) in comparison to other forms of metals. However, metal sulfides may be mobilized (re-oxidized) upon dredging or re-suspension. Previous studies have suggested that the ratio of simultaneously extractable metals (SEM) and acid volatile sulfide (AVS) could be used to predict heavy metal bioavailability in sediments. SEM/AVS ratio, however, does not represent fully the metal sulfide chemistry in sediments and AVS does not represent total sulfides. Furthermore, measurement of multi-elemental SEM is a tedious task. I propose here a total simultaneous extractable metals (TSEM)/total sulfide (TS) ratio to replace the SEM/AVS ratio. I also propose a Cu sulfide index (Cu-SI) to approximate the TSEM/TS radio because the former is simpler to measure. The principle, application and examples of how TSEM/TS and Cu-SI are proper chemical indicators for heavy metal availability are discussed.