This study was carried out to assess the levels of trace metals (Fe, Zn, Mn and Cu) in the macroalgae and sediment of the Sundarban mangrove estuary in Bangladesh. In this connection, macroalgae, water and sediment samples were collected seasonally (pre-monsoon, monsoon and post-monsoon) for a year from the study area. The surface water of the estuary was found to be quite rich in NO3, PO4 and NH4, which is more than that of the sediment pore water. Trace elements were determined using an atomic absorption spectrophotometer. The amount of trace metals in the samples were found in the order of Fe > Mn > Zn > Cu. Enrichment factor was done for trace metals in sediment and showed non-crustal origin of Zn and Cu in the monsoon period. Analysis of variance revealed the seasonal variation of trace metal concentration in sediment (except Mn; p > 0.05) and macroalgae (except Zn; p > 0.05). Iron in sediment showed significant positive correlation both with Fe (r = 0.84, p < 0.05) and Mn (r = 0.87, p < 0.01) in macroalgae. Similarly, Cu in sediment demonstrated a significant positive correlation with Cu in macroalgae (r = 0.81, p < 0.01). The findings reveal a significant communication of metals in sediment and macroalgae.