Leucine-rich alpha-2 glycoprotein (LRG) is a novel biomarker for monitoring disease activity in inflammatory bowel disease (IBD). The aim of this study was to evaluate its utility in monitoring disease activity. In this retrospective study based on case records between August 2020 and July 2021 at our two centers, we examined the correlation between serum levels of LRG and C-reactive protein (CRP) with disease activity in IBD patients. Background factors related to serum LRG levels were also analyzed. Overall, 47 Crohn's disease (CD) and 123 ulcerative colitis (UC) patients were evaluated. In patients with CD, LRG and CRP levels correlated with Harvey-Bradshaw Index (HBI) and Simple Endoscopic Score for CD (SES-CD) (LRG and HBI, r = 0.397; LRG and SES-CD, r = 0.637; CRP and HBI, r = 0.253; CRP and SES-CD, r = 0.332). In patients with UC, LRG and CRP significantly correlated with the partial Mayo score (PMS) and Mayo endoscopic subscore (MES) (LRG and PMS, r = 0.3; CRP and PMS, r = 0.282; LRG and MES, r = 0.424; CRP and MES, r = 0.459). In CD patients with normal CRP, serum LRG level was significantly higher in those with mucosal inflammation than in those with mucosal healing (16.4 vs. 10.7 μg/ mL). Stenosis was associated with serum LRG levels in CD group using multiple regression analysis. Therefore, LRG is a useful biomarker for monitoring disease activity and mucosal inflammation, and indicates the status of intestinal stenosis in IBD patients.