Introduction Pre-emptive scalp infiltration with local anaesthetics is the simplest and most effective method to prevent postoperative incisional pain. However, local infiltration of an anaesthetic only provides relatively short-term pain relief. Methylprednisolone (MP) treatment, administered as an adjuvant at the wound site, has been shown to provide satisfactory pain management after lumbar laminectomy. However, there is no evidence regarding the efficacy of MP infiltration for the relief of postoperative pain after craniotomy. Currently, postoperative pain after craniotomy in children is undertreated. Therefore, we aim to investigate whether pre-emptive scalp infiltration with ropivacaine (RP) plus MP is superior to RP alone to improve postoperative pain after craniotomy in children. Methods and analysis The RP/MP versus RP trial is a prospective, single-centre, randomised, parallel-group study of 100 children aged 8-18 years undergoing intracranial surgery. Participants will be randomly allocated to receive pre-emptive scalp infiltration with either RP plus MP or RP alone. The primary outcome will be the cumulative fentanyl dose administered by patient-controlled intravenous analgesia within 24 hours postoperatively. The secondary outcomes will include postoperative Numerical Rating Scale scores, pain control satisfaction scores, length of stay and adverse events. Data will be analysed by the intention-to-treat principle. Ethical approval and dissemination The study protocol has been approved by the Institutional Review Board of Beijing Tiantan Hospital Affiliated to Capital Medical University (Approval Number: KY 2018-066-02). The results will be disseminated in international academic meetings and published in peer-reviewed journals. Trial registration number NCT03636165; Pre-results. © 2019 BMJ Publishing Group Limited.