Bronchioloalveolar carcinoma (BAC), a subtype of non-small cell lung cancer, is a difficult disease to treat with low response rates with cytotoxic chemotherapy. Bortezomib, a proteasome inhibitor, has demonstrated objective responses in patients with BAC in early-phase clinical trials. We conducted a phase II study of bortezomib in patients with advanced-stage BAC. Patients with advanced BAC, adenocarcinoma with BAC features or BAC with adenocarcinoma features, and less than two prior regimens were eligible. Prior epidermal growth factor receptor (EGFR) inhibitor therapy was allowed. Bortezomib was administered intravenously at 1.6 mg/m2 on days 1 and 8 of every 21-day cycle until disease progression or unacceptable toxicity. The primary end point was response rate. The Simon two-stage design was used. Forty-two patients were enrolled, and the study was halted early for slow accrual. Patient characteristics were female 55%, median age 68 years, and Eastern Cooperative Oncology Group performance status of 0 and 1 in 31 and 11 patients, respectively. Twenty-six (62%) patients had received prior therapy with an EGFR inhibitor. A median of four cycles of therapy were administered. Objective responses were noted in 5%, whereas 57% had disease stabilization. The median progression-free survival and overall survival were 5.5 and 13.6 months, respectively. Grade 3 diarrhea and fatigue were noted in three and five patients, respectively. Bortezomib is tolerated well and is associated with modest anticancer activity in patients with advanced BAC, including patients who progressed on EGFR inhibitor therapy.