We report a case of Descemet's membrane detachment, a rare complication of viscocanalostomy. During the operation, the injection cannula was directed slightly oblique to the Schlemm's canal rather than parallel to it. Localized corneal whitening developed adjacent to the injection site during viscoelastic injection. One week postoperatively, corneal edema decreased and Descemet's membrane detachment was noted. Nine months after surgery, the cornea was clear while the Descemet's membrane detachment remained. And IOP was 19 mmHg without any medications. We think that improper cannula positioning during viscoelastic injection may cause Descemet's membrane detachment, a rare complication of viscocanalostomy.