<p>Using the satellite altimeter data from 1993 to 2021, this study investigates the seasonal and interannual variations of Kuroshio surface water intrusion into the East China Sea (ECS) with an emphasis on transports across different isobaths. The results reveal that the intrusion variability differs among the isobaths used to identify the intrusion. On the seasonal scale, the transport volume and proportion of intrusion into the outer shelf (across 200 m isobath) are greatest in spring compared to other seasons possibly because of the relief of northerly monsoon and the increase of Kuroshio transport. However, in the inner shelf regions (across 100 m isobath), the strongest intrusion occurs in summer, with a much longer residence period and broader spatial range, though the Kuroshio moves farthest away from the coast. This implies that the Kuroshio may have the highest exchange efficiency with the ECS shelf water during summer. On the interannual scale, increased upstream transport from the Kuroshio and shoreward movement of the current almost equally contribute to the enhancement of surface water intrusion into the outer shelf regions. In contrast to the seasonal characteristics, the interannual intrusion into the shallower shelf regions (across the 120 m and 100 m isobaths) is primarily correlated to the position of the Kuroshio axis, i.e., the closer to the coast the Kuroshio is, the more water can enter the inner continental shelf. This result highlights that the importance of factors that control the intrusion variabilities may also change between seasonal and interannual time scales when different isobaths are used.</p>