Background/Aims: Inflammatory bowel disease (IBD) patients frequently have zinc deficiency. IBD patients with zinc deficiency have higher risks of IBD-related hospitalization, complications, and requiring surgery. This study aimed to examine the effectiveness of zinc acetate hydrate (ZAH; Nobelzin) in IBD patients with zinc deficiency. Methods: IBD patients with zinc deficiency who received ZAH from March 2017 to April 2020 were registered in this two-center, retrospective, observational study. Changes in serum zinc levels and disease activity (Crohn’s Disease Activity Index [CDAI]) before and after ZAH administration were analyzed. Results: Fifty-one patients with Crohn’s disease (CD, n = 40) or ulcerative colitis (UC, n = 11) were registered. Median serum zinc level and median CDAI scores significantly improved (55.5–91.0 μg/dL, P< 0.001; 171.5–129, P< 0.001, respectively) in CD patients 4 weeks after starting ZAH administration. Similarly, median serum zinc levels and CDAI scores significantly improved (57.0–81.0 μg/dL, P< 0.001; 177–148, P= 0.012, respectively) 20 weeks after starting ZAH administration. Similar investigations were conducted in groups where no treatment change, other than ZAH administration, was implemented; significant improvements were observed in both serum zinc level and CDAI scores. Median serum zinc levels in UC patients 4 weeks after starting ZAH administration significantly improved from 63.0 to 94.0 μg/dL (P= 0.002), but no significant changes in disease activity were observed. One patient experienced side effects of abdominal discomfort and nausea. Conclusions ZAH administration is effective in improving zinc deficiency and may contribute to improving disease activity in IBD.