Objective: To provide high-quality clinical evidence of the efficacy of Tibetan medicine Honghua Ruyi (HHRY) pills for endometriosis-associated dysmenorrhea. Methods: This study constitutes a multicenter, randomized, double-blind, placebo-controlled trial encompassing a three-menstrual cycle intervention followed by a three-menstrual cycle follow-up period. A total of 164 eligible females with endometriosis-associated dysmenorrhea were randomly divided into HHRY pills and placebo groups in a 1:1 ratio. The primary outcome included dysmenorrhea symptoms assessed using Visual Analog Scale (VAS) scores and quality of life, whereas the secondary outcome measures included the maximum VAS for non-menstrual pelvic pain, duration of pain episodes (in days), frequency and quantity of the consumption of ibuprofen sustained-release capsules (or other non-steroidal anti-inflammatory drugs), and days off work/study for staff/student due to dysmenorrhea, ovarian cyst, and/or pelvic nodule size. The safety was monitored throughout the treatment period. All the analyses were based on the intention-to-treat principle. For continuous outcomes, simple or multiple linear regressions were used to estimate the differences between the HHRY pills and placebo groups, with categorical data expressed as the number and percentage of occurrences. Differences were compared using the chi-square test or Fisher's exact test. The predefined analysis was adjusted for concomitant treatment, a variable considered to be associated with outcomes but unaffected by treatment allocation. Estimates of treatment effects were reported with 95% confidence intervals. Two-tailed P values ≤ .05 were considered statistically significant. Conclusion: Positive results from this trial, upon completion would provide robust evidence for the efficacy and safety of HHRY pills in treating dysmenorrhea in patients with endometriosis.