Acquired non-accommodative comitant esotropia (ANAET) represents a distinct subclass of esotropia that predominantly manifests in older children and adults. Injection of Botulinum Toxin A (BTX) to the extraocular muscle has been used to treat strabismus and a variety of other ocular conditions. In this study, we aimed to evaluate the long-term effectiveness of BTX injections for treating ANAET. In the Department of Ophthalmology at Seoul National University Bundang Hospital between the years 2010 to 2022, a total of 42 patients diagnosed as ANAET with a distant angle of esodeviation ≤ 25 PD and treated with BTX injection were retrospectively reviewed. Data collected from the patients' records included the angle of distant and near esodeviation before injection, post-treatment ocular alignment at distance and near at 2 weeks, 3 months, 6 months, 1 year, and the last follow-up examination, the number of injections and dosage of BTX, and complications after treatment. Treatment was considered successful if the final ocular alignment showed esophoria of 6 PD or less during distant fixation. The baseline esodeviation, determined by the maximum angle of esodeviation at distance before the first BTX injection, was 14.5 ± 5.6 PD. The mean duration from the last BTX injection to the final outpatient visit was 23.7 ± 16.1 months. The treatment success rates for all patients were 90.5% (38/42) at 6 months, 76.2% (32/42) at 1 year, and 73.8% (31/42) at the final examination. By multivariate analysis, the baseline angle of esodeviation (p = 0.008) was the only significant factor related to final success. BTX injection can be a highly favorable therapeutic option for ANAET patients. Specifically, if the maximum angle of deviation in ANAET patients is 15PD or less before treatment, it is advisable to attempt BTX therapy as a first-line treatment option for long-term success.