Objective: To evaluate the efficacy of an inspiratory muscle training protocol on inspiratory muscle function, functional capacity, and quality of life in patients with asthma. Design: A single-blind, randomized controlled clinical trial. Setting: Community-based. Subjects: Patients with asthma, aged between 20 and 70 years old, non-smokers. Interventions: Participants were randomized into two groups: inspiratory muscle training group performed inspiratory muscle training 5 days a week for 8 weeks, consisting of six sets of 30 breaths per day with a training load ⩾50% of maximal inspiratory pressure, plus an educational program; the control group only received the educational program. Main measurements: Maximal inspiratory pressure, inspiratory muscle endurance, and the distance performed on the incremental shuttle walking test were assessed pre-intervention, post-intervention and at follow-up (3 months after the end of the intervention). The asthma quality of life questionnaire was applied pre and post-intervention. Results: Data from 39 participants were analyzed. Maximal inspiratory pressure in percentage of predicted and endurance test duration were significantly higher post-intervention in the inspiratory muscle training group (∆ post–pre: 50.8% vs 7.3% of predicted – P < 0.001 and ∆ post–pre: 207.9 seconds vs 2.7 seconds – P < 0.001, respectively). There was no significant difference in the incremental shuttle walking distance between groups (∆ post–pre: 30.9 m vs −8.1 m, P = 0.165). Quality of life was perceived as significantly better, without a difference between groups ( P > 0.05). Conclusions: About 8 weeks of inspiratory muscle training in patients with controlled asthma significantly increased inspiratory muscle strength and endurance.