In clinical practice of interstitial lung diseases, the establishment of biomarkers useful for predicting prognosis is awaited. We aimed to quantitatively evaluate the development of traction bronchiectasis on chest high-resolution CT images and elucidate its relationship with lung function decline and outcome of the patients. Ten consecutive patients with interstitial pneumonia were subjected. We measured the lumen area of the right B7 bronchus on the CT images taken at the initial and follow-up visits using Ziostation 2 (Ziosoft Inc., Tokyo, Japan) and examine whether the rate of change is associated with the changes in the lung function. The correlation coefficient (rs) was used to examine the relationship between the development of bromchiectasis and declines in %VC and %DLco, and the relationship with the presence or absence of exacerbation and death within 5 years was verified by logistic analysis. The median age of the patients was 73 years old. Five of them received antifibrotic agents, and six experienced acute exacerbation, including 3 fatal cases. Median lung functions at the initial visit were %VC 89.3% and %DLco 68.4%. The median interval between CT scans was 6.7 months. The median increase rate of the lumen area was 12.3%, and there was no significant correlation between the changes in the lumen area and the decline rate of VC (rs = 0.06, p = 0.88) or DLco (rs = -0.17, p = 0.71). The increase rate of the lumen was not associated with exacerbation (OR 1.02, 95%CI 0.94-1.11, p=0.48) or death (OR 1.01, 95%CI 0.92-1.11, p=0.71). In the present study, the development of traction bronchiectasis was not associated with the lung function decline or patient outcome.