AIM: To compare frontalis sling and tarsoconjunctival mullerectomy plus levator resection (TCMLR) in subjects with severe unilateral congenital ptosis with poor levator function (LF). METHODS: A prospective non-randomized non-blinded single center clinical trial. Fifty patients with severe unilateral congenital ptosis with poor LF were recruited. The frontalis sling and TCMLR were performed and the functional, cosmetic outcomes, complications, and success rate were evaluated at 1, 3, and 6mo postoperatively. The t-test, Chi-square, Fishers exact, and nonparametric Mann-Whitney tests were used by SPSS software. RESULTS: Frontalis sling and TCMLR procedures were performed on 26 and 24 patients respectively. The mean age was 10.97±10.67y. LF was significantly better in the TCMLR group at months 1, 3, and 6 (P=0.002). Lagophthalmos was more common in the TCMLR group (no significant difference). At month 3, mild punctate epithelial erosions were observed more in the frontalis sling group (P=0.002). Significant complete success rate of 1st and 6th month for the frontalis sling vs TCMLR groups were 50% vs 20.8% (P=0.02), and 38.4% vs 50% (P=0.03) respectively. CONCLUSION: Complete success rate of TCMLR is higher in long-term follow-up in contrast with the frontalis sling in the short-term. Transient complications are more detected in mid-term follow-ups in both groups.