Background The safety and efficacy of dexmedetomidine for epidural labor analgesia have been reported in numerous literatures, but the optimal dose has not been fully determined. The objective of this study was to determine the dose-response relationship of epidural dexmedetomidine (combined with ropivacaine) for labor analgesia. Methods A total of 120 full-term laboring parturients requesting epidural labor analgesia were enrolled in the study from July 5, 2020 to September 22, 2021. The parturients were randomly assigned to receive 0, 0.1, 0.2, 0.3, 0.4 or 0.5 μg/mL dexmedetomidine combined with 0.075% ropivacaine epidurally. An effective dose was defined as numerical rating scale (NRS) pain score ≤3 at 30-minutes of epidural drug injection. The dose-response relationship of dexmedetomidine (with ropivacaine) for epidural labor analgesia was performed using probit regression. The median effective dose (ED 50 ) and the 95% effective dose (ED 95 ) values for epidural dexmedetomidine combined with 0.075% ropivacaine with 95% confidence intervals (CIs) were derived by interpolation. Results The estimated values of ED 50 and ED 95 with 95% CIs for epidural dexmedetomidine (combined with 0.075% ropivacaine) were 0.085 (0.015 to 0.133) μg/mL and 0.357 (0.287 to 0.493) μg/mL, respectively. No differences were found among groups for sensory block level, number of parturients with Bromage score >0, total dosage of analgesics, cesarean delivery rate, fetal birth weight, Apgar score at 1-minute, Apgar score at 5-minutes and adverse effects. Compared with other groups, group dexmedetomidine 0.5 μg/mL had a longer duration of the first stage of labor. Conclusion The ED 50 and ED 95 values of dexmedetomidine for epidural labor analgesia was 0.085 and 0.357 μg/mL under the conditions of this study. Dexmedetomidine is a suitable adjuvant for epidural labor analgesia.