Exports of oysters from Japan have increased in recent years. However, the current domestic norovirus testing method for oysters prior to export has some technical challenges, mainly in terms of sensitivity. In this study, to examine the performance of testing methods expected to have higher sensitivity than the current domestic method, we compared the sensitivity of the “Standard method,” a newly developed method in Japan, and the ISO 15216 method by quantifying the norovirus genogroup I (GI) and GII. The limit of detection 95 and the limit of quantification were statistically determined using serial dilutions of oyster digestive glands artificially contaminated with norovirus according to the guidance note of the European Union reference laboratory. The ISO method was more sensitive for the detection and quantification of GII than the Standard method. No significant differences were observed between the two methods in the values obtained from quantifying norovirus GI and GII at three different concentrations. These results indicate that the ISO method is more suitable for pre-export testing in Japan.