Background <p>The potential association between birthweight and adult lung function has been postulated, yet the precise nature of this association in later life remains inconclusive.</p> Methods <p>The analysis included 201,615 individuals from the UK Biobank dataset. To identify birthweight subgroups differences in lung function, propensity score matching and a pairwise t-test were conducted. The association between birthweight and lung function was assessed using a linear regression, gradually adjusting for variables. Subgroup analyses were conducted to investigate whether the relationship between birthweight and lung function was modified by variations in age-related lung function changes.</p> Results <p>The low birthweight group demonstrated significantly lower forced expiratory volume in 1&#xa0;s (FEV1) and forced vital capacity (FVC) in comparison to those in the adequate birthweight group (<i>P</i> &lt; 0.001). Conversely, no statistically significant distinction was observed in macrosomia. A positive linear correlation between birthweight and lung function was observed within each interval. In the adequate birthweight group, every 1 Kg increase in birthweight was found to be significantly associated with a mean increase in FEV1 of 70.9 mL in males and 56.0 mL in females. Additionally, there was a significant increase in FVC of 86.7 mL in males and 62.2 mL in females. Macrosomia group demonstrated a more pronounced decrease in lung function, in contrast to the adequate birthweight group which exhibited a similar decline pattern to the low birthweight group.</p> Conclusion <p>Our study suggests an association between optimal birthweight and later-life respiratory health, as observed through stringent statistical analysis.</p>