Background Among respiratory diseases, asthma is one of the most burdensome disorder worldwide. Growing evidence disclose gut dysbiosis may contribute to asthma via the gut-lung axis. Constipation can lead to alteration of the gut microflora. The clinical impact of constipation on asthma has not been researched. Therefore, we aim to assess the risk of asthma in constipated patients by a nationwide population-based cohort study. Methods We analyzed 82421 constipated patients and 82421 individuals without constipation between 1999 and 2013 from the Taiwanese National Health Insurance Research Database. Analysis of propensity score was utilized to match age, gender, comorbidities, and medications at a ratio of 1:1. Besides, multiple Cox regression analysis was performed to evaluate the adjusted hazard ratio of asthma. Furthermore, sensitivity tests and a stratified analysis were conducted. Results The incidence of asthma was 10.8 per 1,000 person-years in the constipation group, which was higher than the rate of 5.6 per 1,000 person-years observed in the non-constipation group. After adjustment for age, gender, comorbidities, and medications, constipated patients had a 1.91-fold greater risk of asthma compared to those without constipation (adjusted hazard ratio [aHR]: 1.91 (95% C.I. 1.84-1.99). In subgroup analyses, patients aged 20-39 years had a 2.04-fold highest risk of asthma in the constipation cohort (aHR:2.04, 95% CI, 1.84-2.26). Besides, the severity of constipation is associated with an increased risk of asthma; the aHR was 1.76 (1.69-1.85), 2.15(2.03-2.27), and 2.29(2.10-2.49) for < 3 times, 3-12 times, and ≥12 times of laxatives prescription within one year, respectively. (p<0.001) Moreover, constipated patients had a higher likelihood of asthma, regardless of gender, comorbidities, and medications. Conclusion Constipation relates to a significantly increased risk of asthma. Physicians should be aware of the possibility of asthma in constipated people. Further research is warranted to investigate the possible pathological mechanisms of this association.