Labor pain is often severe, and analgesic medication may not be indicated. In this randomized controlled trial we examined the effects of music on sensation and distress of pain in Thai primiparous women during the active phase of labor. The gate control theory of pain was the theoretical framework for this study. Randomization with a computerized minimization program was used to assign women to a music group (n = 55) or a control group (n = 55). Women in the intervention group listened to soft music without lyrics for 3 hours starting early in the active phase of labor. Dual visual analog scales were used to measure sensation and distress of pain before starting the study and at three hourly posttests. While controlling for pretest scores, one-way repeated measures analysis of covariance indicated that those in the music group had significantly less sensation and distress of pain than did the control group (F (1, 107) = 18.69, p <.001, effect size =.15, and F (1, 107) = 14.87, p <.001, effect size =.12), respectively. Sensation and distress significantly increased across the 3 hours in both groups (p <.001), except for distress in the music group during the first hour. Distress was significantly lower than sensation in both groups (p <.05). In this controlled study, music--a mild to moderate strength intervention--consistently provided significant relief of severe pain across 3 hours of labor and delayed the increase of affective pain for 1 hour. Nurses can provide soft music to laboring women for greater pain relief during the active phase when contractions are strong and women suffer.