Length–weight relationships (LWRs) were estimated for five fish species in the Fuyuan reach of the middle reaches of Heilongjiang River, northeast China. Fishes were captured using a variety of nets (i.e. drift gill net, set net, fishing cage, fishing jig and fishhook). In addition to November–April, samples were collected monthly from May 2013 to October 2014. The five species were: Lethenteron reissneri, Pelteobagrus ussuriensis, Hemibarbus maculates, Xenocypris macrolepis and Chanodichthys erythropterus. LWRs for Lethenteron reissneri and Pelteobagrus ussuriensis were unknown to FishBase. The a values obtained ranged from 0.0019 (Lethenteron reissneri) to 0.0177 (Pelteobagrus ussuriensis), and b values ranged from 2.710 (Pelteobagrus ussuriensis) to 3.397 (Chanodichthys erythropterus).