Pseudomembranous colitis is a dangerous but unusual side effect of antibiotics usage. We report a case of pseudomembranous colitis that developed in a 50-year-old female patient with diabetes mellitus during first line anti-tuberculous therapy including rifampicin. The patient was diagnosed with active pulmonary tuberculosis 70 days earlier. On admission, she suffered intermittent abdominal pain and watery diarrhea for 2 weeks. Colonoscopy revealed exudative, punctuate, raised plaques with skip areas or edematous hyperemic mucosa, and histopathologic findings were consistent with pseudomembranous colitis with typical volcano-like exudate. Symptoms improved on treatment with metronidazole. There was no recurrence after reinstitution of the anti-tuberculous agents excluding rifampicin. In patients with persistent diarrhea receiving anti-tuberculosis treatment, rifampicin associated pseudomembranous colitis should always be kept in mind.