A study was conducted to examine the effect of standardised ileal digestible (SID) sulphur amino acids/lysine ratio (SAA/Lys) on performance and expression of methionine adenosyltransferase 1 and 2 alpha (MAT1α and MAT2α), and cystathionine gamma-lyase (CTH) in piglets challenged with an enterotoxigenic Escherichia coli (ETEC). Thirty five [Duroc × (Yorkshire × Landrace)] piglets (6.9 ± 0.5 kg) were randomly assigned to five dietary treatments. The diets were antibiotic free with SID SAA/Lys of 48%, 54%, 60%, 66%, and 72%. Pigs were orally challenged with 6 and 15 mL of ciprofloxacin-resistant ETEC K88 on days 7 and 10. Blood samples were collected before (BC) and 6, 24, and 48 h after challenge (AC). Body weight gain and feed intake were collected on days 0, 6, and 12 to determine average daily gain (ADG). Gain to feed ratio (G/F) was calculated by dividing ADG by average daily feed intake (ADFI). On day 13, all pigs were euthanized to collect liver and ileal samples to analyse gene expression using real-time polymerase chain reaction. Pigs fed the diet containing SAA/Lys of 66% had the highest ADG, ADFI, and G/F BC. However, ADG, ADFI, and G/F were similar across all ratios AC. Serum tumor necrosis factor alpha concentration at 6 h AC was higher (P < 0.05) than BC and was improved with increasing SAA/Lys. Increasing SAA/Lys quadratically increased (P < 0.01) CTH and MAT1α expression. Ileal expression of CTH and MAT2α were quadratically increased (P < 0.05) with increasing SAA/Lys. In conclusion, SAA/Lys of 60% is suggested to be optimum for piglets to tolerate ETEC pathogenic challenge.