Length‐weight relationships (LWR) were calculated for seven fish species from the Wutong River, northeast China(47°58'‐47°10'N; 130°07'‐130°48'E), including Ladislavia taczanowskii Dybowski, 1869; Gobio cynocephalus Dybowski, 1869; Rhynchocypris lagowskii (Dybowski, 1869); Lefua costate (Kessler, 1876); Cobitis lutheri Rendahl, 1935; Cobitis sibirica Gladkov, 1935; Perccottus glenii Dybowski, 1877. All fish specimens were collected by electric fishing gear (voltage, 12 V) and gillnets (mesh size: 1.1 cm × 1.1 cm, 1.4 cm × 1.4 cm, 1.8 cm × 1.8 cm, 2.5 cm × 2.5 cm) from May to July 2017. The a values ranged from 0.0038 (Cobitis lutheri) to 0.0084 (Lefua costata), and b values from 2.716 (Lefua costata) to 3.450 (Perccottus glenii) and r2 values from 0.973 (Cobitis lutheri) to 0.995 (ladislavia taczanowskii). This study provides the first published the LWRs for the five species, and new maximum total lengths were recorded for two species, including Gobio cynocephalus and Lefua costata.