Introduction: Amyotrophic lateral sclerosis (ALS) is a progressive, fatal, neurodegenerative disease. Although the pathogenesis remains unresolved, oxidative stress is known to play a pivotal role. Edaravone works in the central nervous system as a potent scavenger of oxygen radicals. In ALS mouse models, edaravone suppresses motor functional decline and nitration of tyrosine residues in the cerebrospinal fluid. Areas covered: Three clinical trials, one phase II open-label trial, and two phase III placebo-control randomized trials were reviewed. In all trials, the primary outcome measure was the changes in scores on the revised ALS functional rating scale (ALSFRS-R) to evaluate motor function of patients. Expert opinion: The phase II open label trial suggested that edaravone is safe and effective in ALS, markedly reducing 3-nitrotyrosine levels in the cerebrospinal fluid. One of the two randomized controlled trials showed beneficial effects in ALSFRS-R, although the differences were not significant. The last trial demonstrated that edaravone provided significant efficacy in ALSFRS-R scores over 24 weeks where concomitant use of riluzole was permitted. Eligibility was restricted to patients with a relatively short disease duration and preserved vital capacity. Therefore, combination therapy with edaravone and riluzole should be considered earlier.