Background: Lung cancer patients are high-risk for active tuberculosis (TB); however, fragility and drug-drug interaction might lead to TB treatment interruption. TB treatment incompletion occurrence and predictors among lung cancer patients remain unclear. Methods: We recruited lung cancer patients with new-onset TB from Taiwan Cancer Registry and Taiwanese National Health Insurance 2007–2015 databases. TB treatment incompletion was the identified primary outcome, and associated risk factors were analyzed. Results: A total of 1155 lung cancer patients with new-onset TB were identified and classified as treatment incompletion (n=706, 61.13%) or completion (n=449). Gender and age distribution was similar in both groups. Under multivariable logistic regression, advanced cancer (stage III and IV) and no first-line TB drugs use were independent factors for treatment incompletion; but older age was not significant. For patients surviving >1 year since TB diagnosis, independent factors for treatment incompletion included no first-line TB drugs use (except pyrazinamide) and absence of hypertension. Cancer stage had borderline significance. Conclusions: TB treatment incompletion occurred in 61.13% of lung cancer patients. Clinicians should carefully titrate anti-TB medications and monitor side effects in lung cancer patients, especially those with treatment incompletion risk factors, to avoid treatment interruption due to fragility and/or drug intolerance.