<p>Marine heatwaves (MHWs) in the East China Sea (ECS), especially those occurring on the ocean bottom (referred to as bottom marine heatwaves, BMHWs), can significantly affect regional ecosystems. However, our understanding of the seasonal variations in the MHWs in the ECS remains limited. This study investigates the characteristics of MHWs in the ECS in summer and winter using high-resolution oceanic reanalysis. Our analyses reveal distinct spatial patterns of BMHWs in these seasons. During summer, the Taiwan Warm Current plays a crucial role in transporting warm water northward, potentially leading to intense BMHWs on the central ECS shelf. These BMHW events usually occur independently of surface warming due to strong stratification in summer. Conversely, winter BMHWs are more prevalent in coastal regions under the influence of coastal currents and typically feature consistent warming from surface to bottom with a deepened mixed layer. These findings inform the coherent vertical structure and driving mechanisms of MHWs in the ECS, which are essential for predicting and managing these extreme events in the future.</p>