Selection response for body weight at marketable size was measured for channel catfish, Ictalurus punctatus, grown in earthen ponds at 7500 fish/ha. Three generations of mass selection for increased body weight in Kansas and Marion strains of channel catfish increased body weight from 453 to 583 g or 29%, and from 530 to 642 g or 21%, respectively, with cumulative realized heritabilities of 0.17 ± 0.016 and 0.19 ± 0.012, respectively. Realized heritabilities for the third generation alone were 0.16 ± 0.016 and 0.23 ± 0.015 for Kansas and Marion strains, respectively. The results indicate that body weight can be significantly increased via mass selection in channel catfish, which should result in increased production and profitability in the catfish farming industry.