Aim Glutamine has various beneficial functions in the gastrointestinal tract. The present study was designed to investigate the effect of two different glutamine supplements on bowel movement at the start of enteral feeding in elderly inpatients. Methods This was a double‐blind, prospective, randomized comparison study. A total of 25 patients aged >75 years recovering from a critical illness in a non‐intensive care unit and scheduled for tube feeding were recruited. Of them, 22 consenting patients were randomly assigned to two groups: glutamine‐fiber‐oligosaccharide treatment group (n = 11) and glutamine F treatment group (n = 11). They were given glutamine three times daily at a dosage of 9 g/day. Enteral nutrition was given at the same dosage to both groups for the duration of the study. The end‐points were stool frequency, Bristol Scale Form Score, bowel function index (Bristol Scale Form Score × stool frequency), the percentage of patients with stool frequency over three per day and those with a BSFS of 6 or 7 in each group. Results There were no significant differences between the two groups in terms of patient characteristics before the study. All the end‐points in the glutamine F group were significantly lower than those in the glutamine‐fiber‐oligosaccharide group. Conclusions Compared with glutamine‐fiber‐oligosaccharide, glutamine F administration resulted in stool hardening and reduced stool frequency in elderly inpatients recovering from acute critical illness in non‐intensive care units. The effects might be caused by the different additive components of glutamine supplements. Geriatr Gerontol Int 2017; ••: ••–••.