Older people with chronic lung diseases and with low physical activity participation rates are at higher risk of morbidity and mortality. This study assessed the feasibility and acceptability of a purpose-designed Internet-based program (ActivOnline) to monitor and encourage exercise and physical activity. Twelve participants with chronic obstructive pulmonary disease or bronchiectasis were recruited (54–84 years). Primary outcome measures were feasibility measured by frequency of program access, and acceptability measured by semistructured interview, system usability scores, and participant perception of benefit. The results suggest regular participation in physical activity and exercise during the 8-week study period and high usability scores (mean = 90% ± 9%). Major themes were the importance of regular exercise and how sustained lifestyle changes were essential to be physically active, regular contact with clinicians assisted with motivation, and aspects of ActivOnline facilitated individual behavior change and confidence to continue exercising. Most participants (82%) reported a benefit from using ActivOnline, and 55% wished to remain on the program indefinitely.