Polonium-210 activity concentration was analysed in the whole body tissue of periwinkle Littorina undulata collected from intertidal rocky shore along Kudankulam coast. We carried out the study for a period of 12months (2011–2012) focusing on three seasons. 210Po was found non-uniformly distributed among the periwinkles depending on the allometry. The 210Po accumulation showed a significant difference between seasons (p<0.05). Smaller sized winkles registered higher activity of 210Po compared to larger ones (p<0.05). The overall activity range of 210Po varied from 13.5 to 58.9Bq/kg (wet). The activity of 210Po was also quantified in seawater and intertidal sediments to calculate the biological concentration factor (BCF) and radiation dose rate. The dose rate to the winkles was performed using ERICA Assessment Tool and it was within the prescribed limit. The intake of 210Po through periwinkles delivered an effective dose in the range of 2.2–9.6μSv/y to human beings.