Ten 50 cm sediment cores were sampled with a D-section corer in the Gulf of Morbihan, France intertidal zone and determined for 210Pbex (excess 210Pb) to estimate the sedimentation and sediment accumulation rates. The activities of 210Pb along with the 208Po tracer were measured by Alpha Spectrometry on a silicon surface barrier detector connected to a multi-channel analyzer. The average activity concentrations of 210Pb in 10 core sediments were ranged from 15.4 to 28.2 Bq kg−1 dry wt. Sedimentation rates were calculated by applying the 210Pb dating method and found to vary between 0.10 and 0.14 cm/year, an average of 0.12 cm/year. This calculation was estimated by selecting the best curve from the concentration of 210Pb (Bq kg−1) distribution with depth and no sediment compaction occurs in the studied cores. This indicates that although the core sediments were obtained within 1 km radius, sedimentation processes differed from location to location due to environmental factors, geomorphology, and sediment types. From the sedimentation rates calculated, the sediment in the upper 50 cm at the Gulf of Morbihan sediment was deposited during the past which ranged from 384 to 509 years. However, if based on the mean sedimentation rates, 0.12 cm/year, sediments in the Gulf of Morbihan had been deposited almost 434 years in the upper 50 cm.