Abstract : Toxic Anterior Segment Syndrome (TASS) is an acute and noninfectious inflammation of the anterior segment. Most cases have been reported as occurring after cataract surgery. Anterior segment inflammation usually occurs within 12-48 hours after surgery, and the symptoms include decreased visual acuity, increased intraocular pressure, corneal edema, anterior chamber (AC) inflammation, fibrin formation, hypopyon, and fixed pupils. The vitreous body is not infected in this syndrome. A 66-years-old male patient came to USU Hospital Medan with chief complaint increased pain and decreased visual acuity. He previously underwent cataract surgery two weeks ago and did not have regular follow up. On examination, the visual acuity was hand movement (OS). Slit-lamp biomicroscopy of the left eye showed hyperemia conjunctiva, minimal edema cornea, and membrane in pupil. On B-scan ultrasonography showed within normal limits. A diagnosis of Toxic Anterior Segment Syndrome was made on left eye. The patient was also immediately administered intracameral moxifloxacin prepared by dilution 0.5 ml, membranectomy and sphincterectomy. This patient was diagnosed with Toxic Anterior Segment Syndrome and treated with membranectomy, sphincterectomy and intracameral moxifloxacin.