The present study focused on the determination of the alpha-emitter, ²¹⁰Po, in two species of marine mussels (bivalve molluscs) commonly available in the southern coastal region of India. The brown mussel, Perna indica was collected from the west coast and the green mussel, Perna viridis from the east coast. The concentration of ²¹⁰Po was related to the allometry (length of shell, wet/dry weight of shell/ soft tissue) of the mussels and significant results were found. The study period focused on three seasons namely, pre-monsoon, monsoon and post-monsoon for a 1-year period (2010-2011). The results revealed higher activity levels in smaller-sized mussels compared to larger ones. Marked variation in ²¹⁰Po activity concentration was noted in the whole-body soft tissues between seasons and sampling site (p < 0.05). The dose rate assessment for mussels was performed using the ERICA Assessment tool. The chronic exposure to mussels due to ²¹⁰Po was found to be lesser than the global benchmark dose rate of 10 mGy h^-1. The effective ingestion dose to adults who intake mussels was estimated to be in the range 5.1-34.9 μSv y^-1. The measurement contributes to the furthering of knowledge of ²¹⁰Po, since no data exist in this region.