This report describes a case of giardiasis detected through stool smear analysis of postoperative stool fluid collected from a high output stoma for obstructive colorectal cancer. The patient, a 67-year-old male, underwent right hemicolectomy with ileostomy for obstructive colorectal cancer. The persistent excessive excretion of postoperative stool fluid from the stoma prompted a stool smear test. The findings revealed the presence of Giardia intestinalis. Fecal output decreased when metronidazole was administered orally. The study strongly recommends that patients with prolonged gastrointestinal symptoms need to undergo stool smear tests.