A bilateral Nuclear Cooperation Agreement (NCA) should define what is subject to the agreement and when. Nuclear Materials (NM) are the subject of NCA with almost all countries, and the definition used in these agreements is borrowed from Article 20 of the IAEA Charter. The IAEA’s definition of NM as consisting of special fissionable material and source material and describes the types of material each contains. In order to control the export of NM under national laws and implement NCA, not only the types of NM but also quantitative criteria are required. This is because controlling small quantities of NM is impossible, unnecessary, and would create excessive administrative burdens. For this reason, the NSG guidelines establish a quantitative threshold of NM requiring control. Nevertheless, no quantitative thresholds have been agreed upon for NM subject to a NCA. Whether NM transferred is subject to the NCA is primarily a matter for the supplier states to determine. The supplier states make the decision based on quantitative criteria defined in their own export control laws. ROK identifies NM that require export licenses by reflecting the same criteria as the NSG guidelines in Foreign Trade Laws and its Notifications. Less than 500 kg of Natural Uranium, 1,000 kg of Depleted Uranium, 1,000 kg of Thorium, and 50 effective grams of special fissionable materials do not require an export license and is therefore not subject to NCA. In the US, the quantitative threshold for requiring an export license is different from that of ROK. For example, special fissionable materials that are not Pu are required if the individual shipment exceed 1 effective gram or 100 effective grams per year. The difference in the quantitative thresholds for NM between the two countries mean that the same item may be subject to NCA under US standards, but not under ROK’s. For example, the export of 8 grams of highly enriched uranium (93%) contained in a neutron detector would not be subject to the NCA in ROK, but would be considered NM subject to a NCA and required a special license in the US. Of course, in order to ensure the application of safeguards and physical protection to all NM transferred between the two countries, the agreement may not include a quantitative threshold for NM. However, the absence of such a threshold can lead to different conclusions by the two countries on the same item and make it challenging to control retransfers. The definition of quantitative standards will be necessary in the supplementary administrative arrangement for the practical control and management of NM subject to the NCA.