This study sought to clarify the extent of segmentectomy that achieves greater lung preservation than lobectomy. This was a single-center retrospective cohort study involving 374 patients with lung cancer who were treated with either lobectomy or segmentectomy between 2013 and 2018. The percentage of preserved pulmonary function (%PPF) after surgery was compared among patients who underwent lobectomy (n = 164), segmentectomy of 2 or more segments (Seg ≥2S; n = 42), and segmentectomy of less than 2 segments (Seg <2S; n = 168). Using perfusion scintigraphy, forced expiratory volume in 1 second of the preserved target lobe was measured to examine its effect on the %PPF. The number of resected subsegments (SSs) in segmentectomy that made the %PPF higher than that observed with lobectomy was also examined. Mean %PPF was lowest in those patients who underwent lobectomy (86%), followed by Seg ≥2S (89%) and Seg <2S (95%) (P < .001), but the difference between the lobectomy and Seg ≥2S was not significant (P = .21). The forced expiratory volume in 1 second of the preserved target lobe was significantly lower in the Seg ≥2S group than in the Seg <2S group (P < .001). The number of resected SSs was 6 to 12 in lobectomy, 4 to 7 in Seg ≥2S, and 1 to 4 in Seg <2S. Although the %PPF after segmentectomy of less than 5 SSs (Seg <5SS) was significantly higher than that after lobectomy (P < .001), the %PPF after segmentectomy of 5 or more SSs (Seg ≥5SS) was not significantly different from that after lobectomy (P = .68). Both the Seg ≥2S and Seg ≥5SS groups did not differ from lobectomy in %PPF because of the low function of preserved target lobe.