This study focuses on the relationship of genetics and Cs-137 radiation doses in Asian green mussel (Perna viridis) collected from Chonburi province, Thailand. They might accumulate the radiocaesium from the nuclear power plants in the Asia-Pacific region incl uding the Fukushima-Daiichi nuclear power plant via their routine or accidental releases. The radiation doses, estimated using ERICA Tool in the bivalves categorized into 3 different size classes including 4-6, 6-8, and 8-10 cm, were below 0.02 μGy/h. In parallel, Micronucleus test and Comet assay were used to investigate genetic responses in the mussels. They revealed minimum micronucleus frequency (MNF) and %Tail DNA varying from 1.80-2.90‰ and 1.36-1.70%, respectively. Our result indicates that neither particular accumulation of Cs-137 nor genetic responses among different size classes of the animals were observed. Furthermore, the radiation doses in the mussels were below the dose limit of 10 μGy/h. Therefore, no radiation effect caused by Cs-137 was found and it was also confirmed by minimal genetic damages. Data obtained can be used as site-specific data for radiological dose and impact assessment and as baseline data to establish the national radiation safety levels to protect Thai marine biota from any possible future nuclear accidents.