A feeding trial was conducted on the effects of methionine hydroxy analog (MHA) and taurine supplementation in diets with high levels of soy protein concentrate (SPC) on the growth performance and amino acid composition of rainbow trout, Oncorhynchus mykiss (Walbaum) comparing with fish meal based diet. The control diet had 520 g kg−1 fish meal. In the methionine deficient diets (5.1 g kg−1), fish meal was replaced by 490 g kg−1 of the SPC in the SPC49 diet. The SPC49 diet was supplemented with either MHA (6 g kg−1) only or a combination of MHA and taurine (2 g kg−1). Fish were fed isoproteic (460 g kg−1) and isolipidic (130 g kg−1) diets for 12 weeks. Growth performance (i.e. weight, feed conversion ratio, and thermal-unit growth coefficient) was inferior in fish fed the SPC49 diet. MHA supplementation improved growth performance (P < 0.05). No difference was observed when taurine was added to the SPC49 and MHA diet (P > 0.05). Whole-body taurine contents increased with taurine supplementation, whereas plasma methionine increased with MHA supplementation (P < 0.05). In conclusion, the substitution of fish meal with SPC supplemented with MHA did not negatively impact growth, and the addition of taurine did not improve growth performance in rainbow trout.