Background/Objectives: Inflammatory bowel diseases primarily encompass Crohn’s disease and ulcerative colitis. Insufficient levels of tryptophan cause an imbalance in the gut microbiota, leading to inflammation in the gastrointestinal tract. The main catabolic pathway of tryptophan is the kynurenine pathway. Our study aims to evaluate serum tryptophan, the kynurenine pathway, and oxidative stress parameters, including total oxidant status and total antioxidant capacity, in patients with Crohn’s disease and ulcerative colitis. Methods: The study included 80 follow-up patients in remission diagnosed with Crohn’s disease and ulcerative colitis who attended the Gastroenterology Outpatient Clinic, as well as 78 healthy controls. Serum tryptophan, kynurenine, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, and kynurenic acid levels were measured with liquid chromatography and tandem mass spectrometry (LC-MS/MS). All statistical analysis was performed using R version 4.2.1. Statistical Language. Results: Serum tryptophan, 3-hydroxyanthranilic acid, and total antioxidant capacity were lower in patients with ulcerative colitis and Crohn’s disease compared to those in the control group. The serum total oxidant status in the control group was significantly lower than in patients with Crohn’s disease and ulcerative colitis. Conclusions: The results of our research indicate that tryptophan and kynurenine pathway metabolites could potentially contribute to the pathogenesis of inflammatory bowel diseases.