Noroviruses are well known as the main causal pathogens of oyster-related outbreaks. To prevent norovirus infection in consuming raw oysters, shellfish farmers generally conduct depuration of oysters to remove the virus before its shipment. However, since the depuration seems to be not effective enough to remove Norovirus from oysters completely, new measures based on different concepts, such as selecting oysters with low capacity to accumulate norovirus, are required to improve the safety to consume raw oysters. In this study, to obtain information for the selecting oysters in which Norovirus are hardly accumulated, we performed an experiment that oysters (Crassostrea gigas) collected from a shellfisheries area were artificially contaminated for 24 h in artificial seawater with a high concentration of Norovirus GII. 2 and GII. 4. After the contamination process, the oysters were depurated in the clean seawater for 24 h. As the result of contamination and depuration, Norovirus GII. 2 (80.0 %) was accumulated in oysters more effectively than GII. 4 (60.0 %). The depuration process only achieved the slight decrease in the percentage of oysters contaminated with GII. 4 from 80.0 % to 60.0 %, while these percentages were higher than in uncontaminated oysters (20.0 %). The difficulty to eradicate Noroviruses accumulated in oysters is consistent with the previous studies. Interestingly, regardless of its genotypes, a part of oysters did not accumulate Norovirus GII during 24 h in the seawater heavily contaminated with this virus. On the other hand, the highest concentration of Norovirus in oysters was 4.08 log copies/g-DT, indicating the huge difference (100 times or higher) in the virus accumulation capability from one oyster to another. The Norovirus GII concentration in oysters was not significantly correlated with the weights of individuals and digestive cecum. This implies the existence of a specific mechanism of virus accumulation which is highly dependent on oyster individuals.