We evaluated the change of corneal endothelium after trabeculectomy with mitomycin-C soaking (0.2 mg/ml, 2.4 ± 1.2 minutes) and the effect of viscoelastic material in reducing this change. In randomly selected cases, 0.05 ml of sodium hyaluronate (Healon®) was injected into anterior chamber (Healon group, n = 20), and same amount of balanced salt solution was injected in the other eyes (Control, n = 18) at the beginning of surgery. There were no differences in clinical variables and specular microscopy result between 2 groups before surgery. After surgery, the change of endothelial cells were significantly reduced in Healon group (cell density; -2.5 ± 1.6%, variability of cell area; 5.8 ± 2.5%, and percentage of hexagonal cell; -2.2 ± 0.7%) compared to control group (-7.7 ± 6.0%, 8.9 ± 4.4%, and -4.8 ± 3.5% respectively, p < 0.01). In trabeculectomy with mitomycin-C, the damage to the corneal endothelium was reduced significantly by injecting the viscoelastic material without significant complication.