The aim of this study was to confirm that the emphysematous changes had increased in the remaining lung on the operation side after lobectomy. Fourteen patients underwent quantitative analysis by computed tomography (CT) and respiratory function testing before and after the operation for upper or lower lobectomy of the lung between March 2005 and May 2007. The degree of emphysema was calculated by dividing the volume of the emphysematous region (CT values: -1,024 to -950 HU) by the volume of the entire lung (CT values: -1,024 to -600 HU) using a 1 mm thickness high resolution CT slice. Comparison by paired t-test showed significant differences between the emphysema rates pre and post operation in the operation side lung (15.3 +/- 7.9% and 21.7 +/- 10.0%, p = 0.02), but there were no significant differences in the contralateral lung (15.8 +/- 7.5% and 17.7 +/- 8.4%, p = 0.25). On the other hand, there was no significant change in the percent forced expiratory volume in one second (FEV1.0%) between pre and post operation (74.4 +/- 10.5% and 75.5 +/- 7.5%, p = 0.60). We consider that it is necessary to note that the emphysematous changes increased in the remaining lung on the operation side after lobectomy even though the FEV1.0% did not decrease at present.