Background To investigate the efficacy and predictability of Muller’s muscle-conjunctival resection (MMCR) with different lengths of tarsectomy for the treatment of unilateral mild-to-moderate blepharoptosis. Methods A retrospective study of patients who underwent MMCR with tarsectomy for unilateral mild-to-moderate blepharoptosis between January 2016 and December 2019 was performed. Individuals with adequate photographic documentation and good levator function were included. Data on age, gender, surgical designs, pre-operative and post-operative marginal reflex distance 1 (MRD1) and tarsal platform show (TPS), and complications were retrieved. Results Sixty patients underwent 8-mm MMCR with 1- or 2-mm tarsectomy; 53 patients (88.3%) showed postoperative symmetry of MRD1 within 1 mm. The average postoperative improvement in MRD1 was 2.15 ± 0.8 mm. Thirty-two patients received 8-mm MMCR with 1-mm tarsectomy (group 1), and 28 patients underwent 8-mm MMCR with 2-mm tarsectomy (group 2). In group 1, postoperative symmetry rate was 90.6%, and the mean elevation of MRD1 was 1.66 ± 0.6 mm. In group 2, postoperative symmetry rate was 85.7%, and the mean elevation of MRD1 was 2.72 ± 0.6 mm. Both groups showed postoperative symmetry of TPS and significant improvement in eyelid position (p < 0.0001). No postoperative complication was noted, and no secondary surgery was needed. Conclusions MMCR with tarsectomy was proven to be a safe, rapid, and effective method for patients with mild-to-moderate ptosis. Predictability and symmetry of the outcome were statistically confirmed. We further suggest a 2.1-mm expected MRD1 elevation as a cut point for choosing between 1- or 2-mm tarsectomy.