Background: Evobrutinib is a highly selective Brutons tyrosine kinase inhibitor targeting B cells and myeloid cells. A phase 2 randomized trial (NCT02975349) in patients with relapsing multiple sclerosis (MS) showed evobrutinib reduced total T1 gadolinium-enhancing lesions over 24 weeks vs placebo. The low annualized relapse rate observed up to week 48 was maintained in a long-term extension. Objectives: To perform a post-hoc analysis of patients with relapsing MS in this phase 2 placebo-controlled trial, evaluating the effect of evobrutinib on blood neurofilament light chain (NfL) level, a biomarker of neuro-axonal damage in MS. Methods: Treatment groups were: placebo; evobrutinib 25 mg once daily (qd); 75 mg qd, 75 mg twice daily (bid). NfL was measured blinded to treatment allocation in samples from baseline and weeks 4, 12, and 24 (Simoa NF-light). The analysis population included all patients with NfL values at baseline and at least one post-baseline. A mixed model for repeated measures (MMRM) identified key variables from an extensive list of baseline covariates that significantly affected log(NfL) over time. The effect of evobrutinib vs placebo on log(NfL) over time was evaluated through MMRM modeling with adjustment for identified baseline covariates. Results: Of 267 patients randomized, 166 (66%) were included in the NfL analysis population. Key selected baseline covariates were age, T2 lesion volume, and Expanded Disability Status Scale score. Relative reductions of NfL levels by 18.9% (P = .010) and 16.8% (P = .040), respectively, were observed with evobrutinib 75 mg bid vs placebo at weeks 12 and 24. For 75 mg qd vs placebo at weeks 12 and 24, relative reductions were 15.4% (P = .043) and 14.1% (P = .10, non-significant), respectively. No difference was observed with 25 mg qd vs placebo. Conclusions: Evobrutinib 75 mg bid significantly lowers blood NfL levels as early as week 12, with reduced levels maintained until 24 weeks, indicating evobrutinib has a beneficial effect on reducing neuro-axonal damage in MS. Role of the Study Sponsor: This study was sponsored by EMD Serono Research and Development Institute, Inc., an affiliate of Merck KGaA, Darmstadt, Germany. The study sponsor was involved in the study design, collection, analysis and interpretation of data, and was involved in the decision to submit the abstract for publication. Involvement of individuals not listed as authors: Medical writing support, provided by Michael Simpson of Bioscript Stirling Ltd, was funded by Merck KGaA, Darmstadt, Germany.