Abstract. River Catfish (Mystus sp.) is a fish that lives in the estuary area of the Blanakan River and has a high level of physiological adaptation to a wide salinity range. River catfish has been consumed by people lived near river. Related to this fact, this study aims to determine the effect of salinity and Zinc (Zn) heavy metals at water on the size distribution of river catfish. The fish samples were collected from 2 stations. The salinity was measured directly from water as well as length and weight of fish. The Zn in water was measured by using AAS (Atomic Absorption Spectroscopy). The results showed that the value of salinity and Zn were 20 ppt - 29 ppt and 0.03mg/l – 0.22 mg/l, respectively. While the ranges for fish length and weight were 13.2 cm – 13.6 cm and 30.6-34.7 gr, respectively. Hence we conclude that the salinity and zinc variation has increasedweight and length of river catfish.