Background: Asthma can have a negative impact on the productivity of paid and unpaid individuals. In this study, we aimed to investigate the impact of salmeterol, which, in recent years, has become available for the treatment of asthma in Japan, on the productivity of patients with asthma. Methods: Relevant data were extracted from the medical records of 54 patients aged ≥15 years with moderate or severe asthma. Loss of productivity was estimated via the human capital approach in the year before and the year after introduction of salmeterol. Results: Lost productivity was significantly reduced (p < 0.001) after salmeterol's introduction compared to the period before its introduction in both paid labors and unpaid ones. Reduced loss of productivity avoided loss of approximately 800,000 yen in the paid ones and 61.3 days in unpaid ones. It was estimated that loss of about 105.4 billion yen in the paid group and 64.5 billion yen in the unpaid group could be avoided if this result was expanded to the wider society. In paid labors, productivity loss was avoided when symptoms were absent during the day, irrespective of the presence or absence of symptoms during the night, whereas, in the unpaid group, the loss was avoided when symptoms were absent during the day or night. Conclusions: It was considered that improvement of clinical symptoms, which occurred in association with the introduction of salmeterol, resulted in avoidance of losses in productivity that had previously occurred in patients with asthma.