Objective. To assess the efficacy of intensive acupuncture (3 times weekly for 8 weeks) versus sham acupuncture for knee osteoarthritis (OA). Methods. In this multicenter, randomized, sham-controlled trial, patients with knee OA were randomly assigned to receive electroacupuncture (EA), manual acupuncture (MA), or sham acupuncture (SA) 3 times weekly for 8 weeks. Participants, outcome assessors, and statisticians were blinded with regard to treatment group assignment. The primary outcome measure was response rate, which is the proportion of participants who simultaneously achieved minimal clinically important improvement in pain and function by week 8. The primary analysis was conducted using a Z test for proportions in the modified intent-to-treat population, which included all randomized participants who had >= 1 post-baseline measurement. Results. Of the 480 participants recruited in the trial, 442 were evaluated for efficacy. The response rates at week 8 were 60.3% (91 of 151), 58.6% (85 of 145), and 47.3% (69 of 146) in the EA, MA, and SA groups, respectively. The between-group differences were 13.0% (97.5% confidence interval [97.5% CI] 0.2%, 25.9%; P = 0.0234) for EA versus SA and 11.3% (97.5% CI -1.6%, 24.4%; P = 0.0507) for MA versus SA. The response rates in the EA and MA groups were both significantly higher than those in the SA group at weeks 16 and 26. Conclusion. Among patients with knee OA, intensive EA resulted in less pain and better function at week 8, compared with SA, and these effects persisted though week 26. Intensive MA had no benefit for knee OA at week 8, although it showed benefits during follow-up.