KRAS mutations in non-small-cell lung cancer (NSCLC) are associated with poor prognosis. Trametinib, a selective inhibitor of MEK1/MEK2, demonstrated similar efficacy to docetaxel in patients with advanced KRAS-mutant NSCLC, with median progression-free survival of 12 and 11 weeks, respectively. With moderate activity as a monotherapy, trametinib-based combination regimens may show improve efficacy. KRAS mutations are detected in 25% of non-small-cell lung cancer (NSCLC) and no targeted therapies are approved for this subset population. Trametinib, a selective allosteric inhibitor of MEK1/MEK2, demonstrated preclinical and clinical activity in KRAS-mutant NSCLC. We report a phase II trial comparing trametinib with docetaxel in patients with advanced KRAS-mutant NSCLC. Eligible patients with histologically confirmed KRAS-mutant NSCLC previously treated with one prior platinum-based chemotherapy were randomly assigned in a ratio of 2 : 1 to trametinib (2 mg orally once daily) or docetaxel (75 mg/m2 i.v. every 3 weeks). Crossover to the other arm after disease progression was allowed. Primary end point was progression-free survival (PFS). The study was prematurely terminated after the interim analysis of 92 PFS events, which showed the comparison of trametinib versus docetaxel for PFS crossed the futility boundary. One hundred and twenty-nine patients with KRAS-mutant NSCLC were randomized; of which, 86 patients received trametinib and 43 received docetaxel. Median PFS was 12 weeks in the trametinib arm and 11 weeks in the docetaxel arm (hazard ratio HR 1.14; 95% CI 0.75–1.75; P = 0.5197). Median overall survival, while the data are immature, was 8 months in the trametinib arm and was not reached in the docetaxel arm (HR 0.97; 95% CI 0.52–1.83; P = 0.934). There were 10 (12%) partial responses (PRs) in the trametinib arm and 5 (12%) PRs in the docetaxel arm (P = 1.0000). The most frequent adverse events (AEs) in ≥20% of trametinib patients were rash, diarrhea, nausea, vomiting, and fatigue. The most frequent grade 3 treatment-related AEs in the trametinib arm were hypertension, rash, diarrhea, and asthenia. Trametinib showed similar PFS and a response rate as docetaxel in patients with previously treated KRAS-mutant-positive NSCLC. NCT01362296.