Aiming to determine the requirements of SID methionine + cysteine (SID Met + Cys) for barrows (15–30kg) 70 pigs (15.216 ± 0.540kg) were used, being distributed in 7 treatments with 5 replicates. A basal diet was formulated to contain 0.52% SID Met + Cys (0.26% SID Met + 0.26% SID Cys). Three treatments consisted in levels of SID Met + Cys (0.58, 0.64, 0.70%) that was maintained the 1:1 ratio between sulfur amino acids (using DL-methionine and L-cysteine) and other 3 treatments consisted in the same levels (0.58, 0.64, 0.70%), but not maintaining the 1:1 ratio (using only DL-methionine), assuring 0.55:0.45, 0.59:0.41 and 0.63:0.37 ratios. Performance, blood parameters, longissimus dorsi muscle depth (LD) and backfat thickness (BF) were evaluated. The sulfur linkages (S-S) in animals’ bristles were determined by using a confocal microscope Senterra Raman. First- and second-degree models were fitted for the levels of SID Met + Cys (0.52, 0.58, 0.64, 0.70%) maintaining or not the 1:1 ratio and the low SID Met + Cys level (basal diet, 0.52%0) was used to fit models maintaining or not the 1:1 ratio. Initial body weight was also included as a covariate. A likelihood ratio test was used to determine the best fitting model (specific models for maintaining or not the 1:1 ratio or a common model for both situations). Linear Response Plateau was used to determine the better SID Met + Cys level when the model of second degree was fitted. The significance level adopted was P < 0.05. The average daily gain (ADG) was affected (P < 0.01) only when the 1:1 ratio was not maintained (using only DL-methionine), reaching a plateau at 0.661% of SID Met + Cys. The LD and BF were not affected. Plasma glucose increased (P < 0.01) and cholesterol decreased (P < 0.01) as SID Met + Cys increased in the diets when supplementing only DL-methionine in the diet. Homocysteine in the blood serum was not affected. In conclusion, barrows from 15 to 30 kg needs 0.661% of SID Met + Cys in the diet (7.88g/day) for a maximum ADG, being not necessary to maintain the 1:1 ratio between SID Met and SID Cys.