The sediment accumulation rates and geochronology of the lagoon sediments were studied from Muthupet, SECI. Accumulation rate was determined by applying a constant rate of supply model (CRS) to the measured ²¹⁰Pb_excess profile. The main objective of this study is to evaluate the age and rate of accumulation of sediments using short-lived radionuclides. Core sampling was carried out at two sites Core 1 and 2 where the samples were taken upto 150 and 175 cm depth respectively, at an interval of 2.5 cm. The age and sedimentation rate of the cores (C1 and C2) were estimated using the depth distribution of radionuclides ¹³⁷Cs, ²¹⁰Pb and ²²⁸Ra determined by high resolution gamma spectrometry on frozen dry samples. The ²¹⁰Pb activity profile in C1 and C2 has a maximum value in few layers beneath the surface sediment. Bottom sediments of C1 (77.5-80 cm) and C2 (117.5-120 cm) depth were dated as the years of 1881 and 1880 respectively. There are two distinct correlations/variations between depth and sediment dates in C1 and C2 from top to the bottom. C1 shows a deflection at peak around 30 cm depth whilst C2 shows maxima at 100 cm depth. Both the cores demonstrate higher values near the surface and tail down to the bottom of the cores.