We aimed to evaluate the prognostic significance of the level of change in SUVmax (Delta SUVmax) on pre and post-treatment PET/CT in early stage non-small cell lung cancer (esNSCLC) patients treated with stereotactic body radiotherapy (SBRT). Between November 2009-February 2018, pathologically proven esNSCLC patients (T1-2NOMO) treated with CyberKnife as primary treatment alone and who had pre and post-treatment PET/CT were retrospectively identified. The ASUVmax was calculated using formula Delta SUVmax= (PreSBRT SUVmax- PostSBRT SUVmax) / (PreSBRT SUVmax). A total of 48 patients were identified. All patients had biopsy-confirmed NSCLC. Median dose was 45 Gy / 3 fr (range: 45-60 Gy / 3-5 fr). According to EORTC metabolic response criteria at 12-16 weeks after SBRT, 8 (16.7%) patients achieved complete response, 35 (72.9%) patients achieved partial response. AUC was calculated as 0.62 for cutoff ASUVmax. Median PFS was 15 (range: 6-54) vs 59 (range: 10-92) months (p= 0.012) and median OS was 36 (range: 10-75) vs 70 (range: 23-92) months (p= 0.045) in patients with Delta SUVmax < 0.62 and >= 0.62, respectively. In both univariate and multivariate analysis, the lower Delta SUVmax (as both dichotomous and continuous variable) was determined as a negative prognostic factor on PFS and it has been showed that the lower Delta SUVmax (only as a dichotomous variable) is a negative prognostic factor on OS in multivariate analysis. In conclusion, in esNSCLC patients who were treated with SBRT, a Delta SUVmax higher than 0.62 demonstrates better PFS and OS.