The purpose of this study was to compare single-port access (SPA) laparoscopy and SPA robot assisted laparoscopy (RAL) for endometriosis with respect to ovarian reserve preservation and surgical outcomes. Clinical factors affecting any reduction in ovarian function after surgery were also evaluated. Patients with endometriosis who underwent SPA laparoscopy (n = 87) or RAL (n = 78) were retrospectively reviewed. Patients’ baseline characteristics, including the severity of endometriosis and surgical outcomes including surgical complexity, were collected. To assess the preservation of ovarian reserve after surgery, serum anti-Müllerian hormone (AMH) levels before surgery, at two weeks, and at three months after surgery were collected. Age, ovarian cyst size, location of cyst, complexity of surgery, and the severity of endometriosis were associated with the reduction in AMH levels after surgery. The severity of endometriosis was higher in the RAL group than in the SPA group. There were no significant differences in other clinical baseline characteristics, including preoperative AMH levels. For surgical outcomes, radical surgery was more frequently performed in the RAL group. In univariate and multivariate linear regression analyses, age, ovarian cyst size, location of cyst, complexity of surgery, and the severity of endometriosis were associated with the reduction in AMH levels after surgery. Incorporating surgical approaches and risk factors for postoperative ovarian function decrease, RAL was more beneficial than SPA laparoscopy for the preservation of ovarian reserve in patients with mild endometriosis (stage I/II) (postoperative 3 month AMH reduction rate (%), SPA laparoscopy vs. RAL, 33.51 ± 19.98 vs. 23.58 ± 14.98, p = 0.04) and in patients who underwent non-complex surgery (postoperative 3 month AMH reduction rate (%), SPA laparoscopy vs. RAL, 37.89 ± 22.37 vs. 22.37 ± 17.49, p = 0.022). SPA RAL may have advantages over SPA laparoscopy in ovarian function preservation, especially in patients with mild endometriosis and patients who have undergone a non-complex surgery.