Stereotactic body radiotherapy (SBRT) delivers precise concentric radiation to a tumor. It is well established that local control depends on the biologically effective dose (BED) delivered, with BED10 of ≥100 as a significant predictor of local control. The aim of this study was to evaluate factors associated with overall survival (OS) in inoperable lung cancer cases treated with SBRT. From 2013 to 2016, 22 patients with inoperable lung cancer treated with SBRT who could be followed up until their time of death were retrospectively enrolled. Data on sex, age, dose (Gray), number of fractions, BED (α/β = 10), pathology, tumor location, performance status, and background lung disease were collected. The median total dose at the isocenter was 50 Gy, and median BED was 120 Gy. OS was compared in groups with BED of ≥120 Gy (“high-BED”; n = 15) and BED of <120 Gy (“low-BED,” n = 7). Overall, 1‑year OS was 48%. In the univariate analysis, the number of fractions, BED, and pathology were significantly associated with OS. The high-BED group showed better OS, with 1‑ and 2‑year OS of 64% and 21%, respectively, compared with 25% and 0%, respectively, for the low-BED group (p = 0.04). No adverse event of grade 3 or higher occurred. For these inoperable lung cancer cases treated with SBRT, BED was significantly associated with OS. The poor OS rate observed in this case series might be associated with the fact that all the tumors were inoperable.