Male Long-tailed Duck in breeding plumage have dark-brownish head, neck, craw, breast and upperparts; head-flanks are grey, eye-ring is white. Feathers of fore-mantle and shoulders have broad buffy edges. Shoulders' feathers are elongated. Belly is white, body-flanks are greyish. Two central tail feathers are much elongated; them length is more 150-200 mm. In winter plumage (from end of October to March-April) male has clear white forehead, crown, throat, craw and rear-neck. Lores and cheeks are grey; neck-flanks with brownish spot. Fore-mantle, wings, mantle and uppertail are dark-brownish. Rear-breast and all other underparts are white, flanks are greyish. Shoulders' feathers are ashy-grey, rear of them are elongated. Base of male's bill is black, its middle part is yellowish-pink, tip is black; legs are greyish, eyes are brownish. Female have black-brown crown, rear-neck, chin and neck-flanks spots. Fore-neck, neck-flanks and eye-area are whitish. Upperparts are dark-brownish; shoulders, wing coverts and uppertail are with whitish edges of feathers. Craw is grey-brown; all other underparts are white. Flight feathers are brownish, tail is greyish. Central tail feathers aren't elongated. Bill is brown green-tinged, legs are greenish-black, eyes are yellowish. Juveniles are similar on female but greyer than it. Sizes: wing 180-240 mm, tarsus 32-38 mm, bill 24-29 mm, females tail 55-70 mm, males tail - up to 250 mm. Weight 650-850 gr.