Background: Dysmenorrhea, dyspareunia and endometriosis-associated pain are considered the main complications in young women with endometriosis. Proscur capsule contains several traditional herbal medicines that have shown anti-inflammatory, antioxidant, anti-androgenic, anti-estrogenic, pelvic pain reducing and analgesic effects in previous pre-clinical and clinical studies. Objective: This study aimed to investigate the clinical efficacy and safety of a standardized polyherbal formulation (proscur) for endometriosis-associated pain in young women with endometriosis. Methods: This study was a single-center, randomized, double-blinded, placebo-controlled, clinical trial. A total of 90 patients aged 20–45 years with endometriosis-associated pain were enrolled. Participants were randomly assigned to the proscur or placebo groups in a ratio of 1:1 and efficacy evaluation was conducted at day 30, 60 and 90. The participants orally administered proscur or placebo two times a day for 12 weeks. The study outcomes were measured based on a change of visual analogue scale (VAS) score and the short form endometriosis health profile questionnaire (EHP-5). Results: We observed an increase in pain relief in women who receive proscur. The serum measures of CA-125 declined in those who received proscur. Intervention was well tolerated, and no serious adverse events occurred. Conclusions: Our study showed that proscur relieved endometriosis-associated pain and CA-125 level with minimal side-effects after treatment. Therefore, proscur combined with standard medical therapy could provide more clinical benefits for patients with endometriosis-associated pain.