This study reports first results on uranium ( 236 U), neptunium ( 237 Np) and plutonium ( 239 Pu and 240 Pu) isotopes in shell samples (i.e. oyster, clam and scallop shells) from the coast of the South of China. The 240 Pu/ 239 Pu and 236 U/ 238 U atom ratios are used for source identification, and the 237 Np/ 239 Pu, 237 Np/ 236 U and 236 U/ 239 Pu non-isotopic atom ratios to study the relative bioaccumulation of Np, Pu and U during the shell formation. The obtained concentration levels are in the 10 4 -10 6 atoms g -1 range in every case. Clear regional differences are observed in the case of the 240 Pu/ 239 Pu atom ratio, with average values lower along the coast of East China Sea (average 0.227 ± 0.120, n = 5) compared to the South China Sea (average 0.258 ± 0.018, n = 7), showing a possible influence of the Pu released at the Pacific Proving Ground nuclear test site. 236 U/ 238 U ( × 10 -8 ) atom ratios range from 0.046 ± 0.009 to 0.524 ± 0.135, in agreement with the expected levels in surface seawater from the China Sea. 237 Np/ 239 Pu (average 4.1 ± 2.6, n = 13) and 237 Np/ 236 U ratios (average 14 ± 10, n = 13) in the oyster shells are clearly enhanced compared to the estimated one in the surface seawater, pointing out higher bioaccumulation of Np compared to Pu and U.