This study seeks to address the limitations in previous related studies on vitamin D replacement and bronchiectasis exacerbation occurrence through a self-controlled pilot study. The investigators aim to investigate whether vitamin D replacement in bronchiectasis patients with vitamin D deficiency can reduce hospitalized bronchiectasis exacerbation occurrence. Patients who participated in the prior study entitled "Prospective clinical study on serum 25-hydroxyvitamin D (25-OH D) level and risk of bronchiectasis exacerbation" (UW 22-317) will be invited for participation during regular clinic follow-up and management in Queen Mary Hospital. If participants are willing to join the further research, participants will be recruited in this self-controlled study. There are some differences from usual management to non-CF bronchiectasis subjects. The study subjects would be checked for their blood 25-hydroxyvitamin-D level during the study period. The non-CF bronchiectasis subjects with Vitamin D deficiency would be given 1000 IU and 2000 IU (if needed). The investigators aim to correct their Vitamin D deficiency completely, aiming at blood 25-hydroxyvitamin-D level >=50, i.e. treat to target. The dose depends on the level of Vitamin D after replacement. If blood 25-hydroxyvitamin-D level is 50 or above, then 1000 IU is suffice. If blood 25-hydroxyvitamin-D level is still below 50, the investigators will increase to 2000 IU.

Inclusion Criteria:

1. ages 18 years or above, male or female.
2. confirmed diagnosis of non-CF bronchiectasis based on high-resolution computed tomography (HRCT) scan.
3. participation in the prior study entitled "Prospective clinical study on serum 25-hydroxyvitamin D (25-OH D) level and risk of bronchiectasis exacerbation" (UW 22-317)

Exclusion Criteria:

1. underlying asthma, COPD and other co-existing respiratory diseases
2. underlying osteoporosis
3. supplementary Vitamin D in their regimen
4. advanced chronic kidney disease with estimated glomerular filtration rate (eGFR) < 30mL/min