Peroral endoscopic myotomy (POEM) is one of the standard treatment modality for achalasia. This study was to evaluate the usefulness of timed barium esophagography (TBE) in the evaluation of treatment effect of POEM for achalasia. A total of 36 patients (M:F=22:14) underwent pre- and post-POEM TBE (3 groups according to lower esophageal sphincter (LES) caliber, A: < 5 mm, B: 5~8 mm, C: > 8 mm). On pre and post-POEM TBE, the rate of area changes of barium column and the changes of LES caliber were investigated. All data were statistically analyzed using the Kruskal-Wallis test or Mann-Whitney U test. The mean rate of area change of the barium column at 5 minutes between pre- and post-POEM TBE were -51.7%, -28.8% and -11.6% in group A (n=10), B (n=18), and C (n=8), respectively, statistically significant (p < 0.001). The rate difference of the barium column area changes between group A and group B only showed the statistical significance (p < 0.001). The mean increased caliber of LES after POEM was 5.5 mm, 2.9 mm, and 3.3 mm in group A, B, and C, respectively. Group A and bird’s beak type showed a statistically significant treatment effect (p < 0.001). In conclusion, TBE was useful in the evaluation of the treatment effect of POEM for achalasia and the narrowest LES group and bird’s beak esophageal type on TBE showed statistically significant treatment effects.