Abstract: Besides having a significant impact on marine wildlife and biodiversity, marine litter can cause serious environmental and economic problems. To understand and alleviate marine litter problems, investigations on marine litter are essential. In April 2023, a simultaneous survey of floating litter and seabed litter was conducted in the waters of Hangzhou Bay using a professional marine environmental survey vessel, and during July to October 2022 a beach litter survey was conducted in four sections of the Hangzhou Bay. The results showed that the average abundance in the studied area was 414 items/km² for large to extra large floating litter, 8446 items/km² for medium-size floating litter, and 10301 items/km² for seabed litter. On average, the floating litter in Hangzhou Bay recorded 0.56 kg/km², and 70.22 kg/km² for seabed litter. The abundance and weight density of floating litter were higher in the inner part of Hangzhou Bay than those in the outer, while for seabed litter the result was reversed. Plastic debris was the most abundant type of marine litter in the area, accounting for more than half of the total abundance. In comparison, the abundance of floating litter in Hangzhou Bay was significantly higher than the national average, but the weight density was lower than the national average, which suggested an overall feature of “small pieces and light weighted”. Assessment for beach cleanliness and degree of plastic debris pollution based on the CCI and PAI indices showed that the four surveyed beaches all reached level “very clean”, Jiuzi beach and Lulanqingsha beach in Daishan county were classified under the category of “very low abundance of plastic debris”, and Zhujiajian beach in Zhoushan city and Jihu beach in Shengsi county under the category of “low abundance of plastic debris” according to the PAI index respectively.