Background. ALDH1A1 (aldehyde dehydrogenase 1 family, member Al) is highly expressed in non-small-cell lung cancer (NSCLC). We assessed the potential clinical value of serum ALDH1A1 in the diagnosis and prognosis of non-small-cell lung cancer. Method. Between 2010 and 2011, serum samples from 100 non-small-cell lung cancer patients before tumor resection, 60 patients with benign lung disease, and 60 healthy volunteers were collected and analyzed retrospectively for ALDH1A1, using sandwich ELISA. We further evaluated the serum and tumor ALDH1A1 levels of non-small-cell lung cancer patients before and after surgery. We compared the diagnostic and prognostic values of serum ALDH1A1 with that of carcinoembryonic antigen. Results. Elevated serum ALDH1A1 levels were observed in 55 of the 100 (55%) non-small-cell lung cancer patients. The ALDH1A1 levels were much higher in patients with advanced stages than in those with early stage tumors. Of the 30 non-small-cell lung cancer patients who underwent surgery, 19 had elevated serum ALDH1A1 levels before surgery, but the serum ALDH1A1 level was undetectable by postoperative day 7. Analysis of receiver operating characteristic curves showed that ALDH1A1 might be better than carcinoembryonic antigen in distinguishing non-small-cell lung cancer from benign disease or the healthy control. Combined application of ALDH1A1 and carcino embryonic antigen significantly increased the sensitivity of carcinoembryonic antigen alone, with an accuracy of 83%. Conclusions. Our results showed that serum levels of ALDH1A1 were correlated with carcinogenesis and progression of non-small-cell lung cancer. Detection of serum ALDH1A1 can be helpful in the diagnosis and prognosis of non-small-cell lung cancer. The diagnosis rate of non-small-cell lung cancer could be significantly improved when carcinoembryonic antigen is combined with ALDH1A1.