Habitat selection of the Endangered Scaly-sided Merganser Mergus squamatus was studied in four rivers of Poyang Lake, Jiangxi Province, China at landscape and micro-habitat scales, from November 2017 to March 2018 and November 2018 to March 2019. At landscape scale, the main foraging habitats of this species include woodlands and farmlands. The largest proportion of woodland in the habitats was 88.70%. Proportion of shoals in foraging habitats at 500-m, 1000-m, 1500-m and 5000-m scales were larger than that in control plots, indicating that the presence of shoals is an important factor determining habitat selection of this bird. At micro-habitat scale, water flow speed (P=0.044), and distance to road (P=0.018) and village (P=0.001) were significantly greater than in control plots. Principal component analysis showed that safety factors (vegetation cover on both banks, distance to a mine factory and river width) were the three most important habitat factors, indicating that Scaly-sided Merganser had high requirements for shelter and safety. Twenty two species of fish belonging to eight families and three orders were identified in foraging areas of the Scaly-sided Merganser. We could identify only six fish species eaten by the merganser viz., Carassius auratus, Misgurnus anguillicaudatus, Noemacheilus fasciolatus, Silurus asotus, Tachysurus fulvidraco and Siniperca chuatsi, which were relatively common and present in all the four rivers, indicating that this bird was an opportunist predator. It is important to reduce human activities and protect woodland and aquatic environments because Scaly-sided Merganser have high requirements for safety and water conditions under both landscape and micro-habitat scales.