Background: To compare the effects of Dilapan-S versus phloroglucinol on cervical dilation in hysteroscopic polyp resection. Methods: This prospective, observational study enrolled non-menopausal patients with endometrial polyps who underwent operative hysteroscopy for transcervical polyp resection between October 2021 and October 2022. The patients were given Dilapan-S or phloroglucinol for cervical dilation. The primary outcome was cervical dilation time; secondary outcomes included cervical softening and adverse events. Non-inferiority was prespecified with a margin of 6 seconds. Results: Among 105 included patients, 55 were given phloroglucinol and 50 Dilapan-S. There were no significant differences in age, body mass index (BMI), history of vaginal delivery, hysteroscopic electrotomy, and cervical conization between the two groups (all p > 0.05). The cervical dilation time in the Dilapan-S group was shorter than in the phloroglucinol group (41.74 \pm 8.68 s vs. 62.04 \pm 9.55 s, non-inferiority p 0.001). Also, more patients achieved highly effective cervical softening in the Dilapan-S group compared to the phloroglucinol group (44/50 vs. 1/55, p 0.001). There were 4 cases of diarrhea (p = 0.103), 12 cases of vaginal bleeding (p 0.001), and 4 cases of abdominal pain in the Dilapan-S group (p = 0.103), and none in the phloroglucinol group. There were also 5 cases of intraoperative water leakage in the phloroglucinol group and 8 cases in the Dilapan-S group (p = 0.283). Conclusions: Dilapan-S is found to be equally effective for cervical dilation as phloroglucinol; however, it is associated with a higher incidence of diarrhea, vaginal bleeding, and abdominal pain complications.