Research at South Dakota State University has previously shown that standard ileal digestibility (SID) values for fish meal and microbially-converted soybean meal (MCSBM) were similar. This study was designed to evaluate MCSBM as a replacement for FM in weaned pig diets. The experiment involved 184 barrows and 152 gilts weaned at 21d of age. The experimental diets were: 1) Control diet containing corn, soybean meal and whey; 2) Control diet + acidifier; 3) Control diet + fish meal; 4) Fish meal+ acidifier; 5) Control diet+ MCSBM; and 6) MCSBM + acidifier. The fishmeal and MCSBM were included at 7.5 and 5.0%, respectively. The pigs were fed the experimental diets for 21 days and fed a common diet for an additional 14 days. Daily gain and gain:feed from day 0 to 7, 8 to 21, and 22 to 35 were not different between treatments. Daily feed intake tended to be greater (P = 0.09) in pigs fed fish meal compared to the control diet (954 vs. 769g/d, respectively), similarly for fish meal compared with MCSBM + acid (954 vs. 756 g/d) from d 22 to 28. Performance was similar for pigs fed fish meal or MCSBM, thus MCSBM may be an alternative to fish meal in nursery diets; however, it is important to note neither fish meal nor MCSBM provided additional benefit over solvent extracted soybean meal in the control treatment.